diff --git a/panel/chat/feed.py b/panel/chat/feed.py
index 70cf1a0fcb..a6c30839a8 100644
--- a/panel/chat/feed.py
+++ b/panel/chat/feed.py
@@ -225,6 +225,8 @@ class ChatFeed(ListPanel):
     _disabled_stack = param.List(doc="""
         The previous disabled state of the feed.""")
 
+    _card_type: ClassVar[type[Card]] = Card
+    _message_type: ClassVar[type[ChatMessage]] = ChatMessage
     _stylesheets: ClassVar[list[str]] = [f"{CDN_DIST}css/chat_feed.css"]
 
     def __init__(self, *objects, **params):
@@ -238,7 +240,7 @@ def __init__(self, *objects, **params):
         # forward message params to ChatMessage for convenience
         message_params = params.get("message_params", {})
         for param_key in params.copy():
-            if param_key not in self.param and param_key in ChatMessage.param:
+            if param_key not in self.param and param_key in self._message_type.param:
                 message_params[param_key] = params.pop(param_key)
         params["message_params"] = message_params
 
@@ -246,7 +248,7 @@ def __init__(self, *objects, **params):
 
         if self.help_text:
             self.objects = [
-                ChatMessage(
+                self._message_type(
                     self.help_text,
                     user="Help",
                     show_edit_icon=False,
@@ -303,7 +305,7 @@ def __init__(self, *objects, **params):
         card_params.update(card_overrides)
         self.link(self._chat_log, objects='objects', bidirectional=True)
         # we have a card for the title
-        self._card = Card(
+        self._card = self._card_type(
             self._chat_log,
             VSpacer(),
             **card_params
@@ -359,7 +361,7 @@ def _update_placeholder(self):
             PLACEHOLDER_SVG, sizing_mode="fixed", width=35, height=35,
             css_classes=["rotating-placeholder"]
         )
-        self._placeholder = ChatMessage(
+        self._placeholder = self._message_type(
             self.placeholder_text,
             avatar=loading_avatar,
             css_classes=["message"],
@@ -436,7 +438,7 @@ def _build_message(
                 (isinstance(user, str) and user.lower() not in (self.callback_user.lower(), "help"))
             )
 
-        message = ChatMessage(**message_params)
+        message = self._message_type(**message_params)
         message.param.watch(self._on_edit_message, "edited")
         return message
 
@@ -863,7 +865,7 @@ def add_step(
             if default_layout == "column":
                 layout = Column
             elif default_layout == "card":
-                layout = Card
+                layout = self._card_type
                 input_layout_params["header_css_classes"] = ["card-header"]
                 title = layout_params.pop("title", None)
                 input_layout_params["header"] = HTML(
diff --git a/panel/chat/interface.py b/panel/chat/interface.py
index 9a450457f7..ddcda3a636 100644
--- a/panel/chat/interface.py
+++ b/panel/chat/interface.py
@@ -163,11 +163,12 @@ class ChatInterface(ChatFeed):
         The rendered buttons.""")
 
     _stylesheets: ClassVar[list[str]] = [f"{CDN_DIST}css/chat_interface.css"]
+    _input_type: ClassVar[type[WidgetBase]] = ChatAreaInput
 
     def __init__(self, *objects, **params):
         widgets = params.get("widgets")
         if widgets is None:
-            params["widgets"] = [ChatAreaInput(placeholder="Send a message")]
+            params["widgets"] = [self._input_type(placeholder="Send a message")]
         elif not isinstance(widgets, list):
             params["widgets"] = [widgets]
         active = params.pop("active", None)
@@ -204,15 +205,7 @@ def _update_input_width(self):
         if self.show_button_name is None:
             self.show_button_name = self.width is None or self.width >= 400
 
-    @param.depends("widgets", "button_properties", watch=True)
-    def _init_widgets(self):
-        """
-        Initialize the input widgets.
-
-        Returns
-        -------
-        The input widgets.
-        """
+    def _init_button_data(self):
         default_button_properties = {
             "send": {"icon": "send", "_default_callback": self._click_send},
             "stop": {"icon": "player-stop", "_default_callback": self._click_stop},
@@ -221,7 +214,6 @@ def _init_widgets(self):
             "clear": {"icon": "trash", "_default_callback": self._click_clear},
         }
         self._allow_revert = len(self.button_properties) == 0
-
         button_properties = {**default_button_properties, **self.button_properties}
         for index, (name, properties) in enumerate(button_properties.items()):
             name = name.lower()
@@ -256,6 +248,16 @@ def _init_widgets(self):
                 js_on_click=js_on_click,
             )
 
+    @param.depends("widgets", "button_properties", watch=True)
+    def _init_widgets(self):
+        """
+        Initialize the input widgets.
+
+        Returns
+        -------
+        The input widgets.
+        """
+        self._init_button_data()
         widgets = self.widgets
         if isinstance(self.widgets, WidgetBase):
             widgets = [self.widgets]
@@ -290,7 +292,7 @@ def _init_widgets(self):
             # TextAreaInput will trigger auto send!
             auto_send = (
                 isinstance(widget, tuple(self.auto_send_types)) or
-                type(widget) in (TextInput, ChatAreaInput)
+                type(widget) in (TextInput, self._input_type)
             )
             if auto_send and widget in new_widgets:
                 callback = partial(self._button_data["send"].callback, self)
@@ -299,7 +301,7 @@ def _init_widgets(self):
                 sizing_mode="stretch_width",
                 css_classes=["chat-interface-input-widget"]
             )
-            if isinstance(widget, ChatAreaInput):
+            if isinstance(widget, self._input_type):
                 self.link(widget, disabled="disabled_enter")
 
             self._buttons = {}
diff --git a/panel/reactive.py b/panel/reactive.py
index 9277898dd2..9fcabc2f9b 100644
--- a/panel/reactive.py
+++ b/panel/reactive.py
@@ -1618,7 +1618,7 @@ def _set_on_model(self, msg: Mapping[str, Any], root: Model, model: Model) -> No
         try:
             model.update(**transformed)
         finally:
-            if old:
+            if prev_changing:
                 self._changing[root.ref['id']] = prev_changing
             else:
                 del self._changing[root.ref['id']]
diff --git a/panel/viewable.py b/panel/viewable.py
index 341007e1f3..f338464a2c 100644
--- a/panel/viewable.py
+++ b/panel/viewable.py
@@ -1261,7 +1261,7 @@ def is_viewable_param(parameter: param.Parameter) -> bool:
     """
     if isinstance(parameter, (Child, Children)):
         return True
-    if isinstance(parameter, param.ClassSelector) and _is_viewable_class_selector(parameter):
+    if isinstance(parameter, param.ClassSelector) and _is_viewable_class_selector(parameter) and parameter.is_instance:
         return True
     if isinstance(parameter, param.List) and _is_viewable_list(parameter):
         return True
diff --git a/panel/widgets/select.py b/panel/widgets/select.py
index 6949a34b8a..6a55a2fad6 100644
--- a/panel/widgets/select.py
+++ b/panel/widgets/select.py
@@ -275,7 +275,7 @@ def _validate_options_groups(self, *events):
             )
 
     def _process_param_change(self, msg: dict[str, Any]) -> dict[str, Any]:
-        groups_provided = 'groups' in msg
+        groups_provided = msg.get('groups') is not None
         msg = super()._process_param_change(msg)
         if groups_provided or 'options' in msg and self.groups:
             groups: dict[str, list[str | tuple[str, str]]] = self.groups