Is there any way in the debug window to suspend when a field (in a table)'s content changes?

I have a form that is changing the description of a lookup table and I need to find the code that is causing it. There is a relationship in my form such that the grid's field is a candidate key. (APINVOIC.ACCOUNT is the primary key of ACCT.ACCOUNT)

Grid
Column1 Column2
Header Account Description
Controlsource APINVOIC.account ACCT.description

In Acct table I have:
1100 Description1
1200 Description2

I enter 1200 in column 1 and column 2 displays the correct description. Then I backtab and replace the 1200 in column 1 with 1100 (which should change the record pointer in the ACCT table to a different record.) The description changes in column 2 to the description which belongs to 1100 - this is correct. At this point I think the record pointer moved correctly and I am pointing to the 1100 record. The problem is that when I look at the data in the ACCT table, I see that :
1200 Description2
1100 Description2

So the original description that went with 1200 (Description1) has been replaced with Description2 and now both of my records have the same description and Description1 is lost so somehow, instead of just moving the record pointer to a different record in the ACCT table, the control has somehow replaced the contents of the description with the second description.

SO... I need to figure out when this is actually happening and therefore I need to put something in the debug window so I can stop at the corresponding code...


Thanks in Advance,

Sandi