I can easily reproduce this problem without a form.

Steps to reproduce error:
1) Open table with primary index and set buffering to 5 (Optimistic Table)
2) APPEND BLANK
3) Go to appended record and fill with valid values (unique key)
4) Use up arrow to go to previous record.
5) Return to new record.
6) Blank out one of the fields that are part of the primary key.
7) Re-enter the same value you just removed.
8) Go to another record. Wham! Error!

Why??? The record seems to be conflicting with itself!

Elyse