Why Combo box default value returns 0 in form

[MajP]

I have looked at this form and tried everything I can think of and even decompiled the database. I have absolutely no idea what is happening and have tried just about everything to get around it. What is happening makes no sense. Yes you should consider a redesign to make this more manageable, but none of that answers why this is happening. The only thing I would try is rebuilding form from scratch.