If a script module calls a function defined in a script that imports this module then this function may or may not be found depending on call scenarios and PowerShell versions.
Test-Module.ps1 imports MyModule.psm1 and
defines the function MyFunction. Then it calls the imported function
Test-MyFunction which is supposed to call MyFunction. This fails in v2
because MyFunction is not found.
In v5 this scenario works as expected. At this point this may create an
illusion that all is fine. But the problem is revealed in a slightly more
complex scenario. When the working script Test-Module.ps1
is called from another script Test-Module2.ps1 then
MyFunction is not found again.
Scripts MyScript.ps1, Test-Script.ps1, and
Test-Script2.ps1 implement the same call scenarios using
dot-sourcing of the function Test-MyFunction. It calls MyFunction fine.