Jason, thanks for creating the support ticket. Due to time difference though, it is hard to find a time which matches your tech support call line. I will reply to the support ticket, but as Rune just confirmed, there is a problem and it would be easier if it was simply fixed.
I did a little more experimentation and found something interesting. Let's say the many to many table is set up like this. id, options_id, main_id. For me, when I insert a record, options_id is fine, but like Rune said, main_id is 0. Then I modified the table to be id, options_id, main_id, pricediff_id - adding the pricecdiff additional field. In the relational table wizard, I set the pricediff_id to a random number. Now the main_id data is writing into the pricediff_id and main_id is still 0.
I will wake up early and get with your engineers early next week.