Invalid Opcode... bug?

[Comperio]

I discovered a problem that I'm not sure is a bug or not. Maybe someone can help me understand this:

Look at this very simplified script:

PHP Code:

name "My Test"
outfile "blah.exe"
ShowInstDetails show

Section
SectionEnd

Function .onInit
  exch $0
  pop $R0
  MessageBox MB_OK "here it is:[$R0]"
FunctionEnd 


If I compile this script, I get no errors. But, when I run the resulting EXE, I get an invalid Opcode error.

By making changing the .onInit function to push $0 (instead of exch $0), then it runs fine.

I've tried assigning values to $0, using $1 instead of $0, and even using my own variable, but each time, I get the Opcode error when I use the Exch call.

ideas?