A Form Region (DEPT) with 2 almost identical Interactive Grids (on EMP) where you can edit EMP details for the current DEPT (identified by item P1189_DEPTNO).
For this demo I hardcoded the value of P1189_DEPTNO (to 10) and disabled the IG processing, but that doesn't really matter here.
What does matter is that the 2 IGs behave differently, which I did not expect (and also don't understand).
The only difference between the IGs is that IG_1 does NOT have P1189_DEPTNO as the "Page Items to Submit", and IG_2 DOES.
Try editing a row in IG_1, click Save, and see the odd behaviour.
If you do the same in IG_2 then everything works fine.
I have no idea why this happens. The value of P1189_DEPTNO is known at all times and does not change, so why should submitting it matter?
Note that both IGs would save the data correctly (if you re-enabled the IG processing of course), so it's only the GUI that gets messed up.
Also note that the Form is needed to get this weird effect. Without the Form but with just a page item P1189_DEPTNO, both IGs work fine. Which only adds to the mystery...