AutoCAD Inventor :: Custom VBA Function In Parameter

I've got a custom VBA function that works perfectly when called from a parameter in my part.

However, when in the context of my assembly, there is no error, but the function no longer runs, and the parameter text is red.

Apparently, the function is no longer in context?

I've heard of external rules, but have never implemented one.

Is there a way to declare my function and keep it in context regardless?
 
Public Function BumpHeight(dblHeight As Double, dblMember As Double) As Double Dim X As Integer X = 2 If dblHeight > dblMember * 2 Then BumpHeight = dblHeight Else BumpHeight = dblMember * X End If BumpHeight = BumpHeight / 2.54 End Function
Here is the Parameter:

 VBA:BumpHeight(ValanceBackBumpoutHeight;ValanceMemberSize) * 1 in

Update: (problem better defined)

What seems to be happening is that once I insert the part into an assembly, it creates a new blank copy of the parts' modules in VBA and the functions no longer work.

If I go to the VBA editor, 

There are now two copies of my part listed in the browser tree, but the new one is blank.

If I paste in my function to the new one, it will work until I return to the parent assembly.

Next time I come back to the part, it will have a new blank set of modules.

This appears to continue indefinitely...

see the attached screenshot.

At this point there are only 2 copies of the DocumentProject. The original still contains my functions, but the new one is blank.

I need these functions to work in order to build my model.