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.
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.
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.
It took me quite a while to figure out what is causing this - and now that I know, I'm still not 100% sure why it's a problem. But at least now I know how to avoid it :-)
The cause turned out to be the Form region; or more specifically, the page items that are created when creating a Form region.
By default, these page items are created with the option "Session State -> Storage" set to "Per Request (Memory Only)".
This is different from normal page items, which have this option set to "Per Session (Persistent)" by default. It never crossed my mind that the default setting for thos page items would be different...
So another fix for this issue could be to set P1189_DEPTNO to "Per Session (Persistent)". But I suppose submitting the page item is just as easy.
To be fair, the Help function does - sort of - indicate this:
Per Request (Memory Only)
Do not save state in the database. State is only available when processing the current request. When AJAX requests need to use an item, make sure to pass the item name via "Page Items To Submit".
Per Session (Persistent)
Maintain for each session by storing the value in the database, to access it across requests.
I suppose the key here is the fact that AJAX is used, which may use a different (or no) session when running? That is a guess which needs further investigation, but it seems logical.