1. When grid's recordsource changes (I always tend to do this programmatically) I usually wrap the code that requery the grid's recordsource (let's say Table1) with a leading
THISFORM.grdMyGrid.RecordSource = ''
and an ending
THISFORM.grdMyGrid.RecordSource = 'Table1'
This way I preserve grid / columns settings that otherwise get lost.

2. In Init() event of main form I coded:
...
*- Set relation into Attachm for selected products lv_orditems.itemcod
SET ORDER TO TAG Item IN Attachm
SET RELATION TO itemcod INTO Attachm IN lv_orditems
...

3. I only bind Attachm table field item to a grid column. Other grid columns are binded to lv_orditems fields. No other controls in the form involves Attachm nor lv_orditems fields.