I just did a quick test with FMPA12. I have the field set to include the arrow for the drop down. I set the field with an OnObjectEnter trigger and opened the debuggger.
If i click in the field and not on the arrow, the debugger runs and i don't get the drop down.
If i click on the arrow, i get the drop down and it remains open while debugging the script.
After testing a few methods i havent found a way to force the drop down. Even scripting a go to field or go to object wont pop the list
Thanks Matt - enabling the arrow at least allows me to debug the script. Thanks for the answer!