>You (and Mike Y) are correct. The next day when I tried it, the columns (having ControlSource equal to memvars) always showed the same value for each row in the grid :( So back to square 1 :) My next approach was to open another instance of my Products.dbf table in the form's DE, and aliased it as "Lookup". I now use Lookup for the ItemNo dropdown combo control. Lookup has no relations defined. But the InvDetail table has a relation defined into Products. So columns like ItemDesc can now be defined with ControlSource=Products.ItemDesc. The end result now works as I had wanted all along...
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>But seeing what a PITA working with grids can be, I went and bought a copy of Codemine... Wish me luck :)

For a moment I didn't notice "copy of" and skimmed straight to "codemine" which sounded like some sort of tough medicine for the head (and against the headache)... and on second glance I got it.

Actually, you hit the full tour of beginner's luck: right on the first step you hit something nasty, that people who use it for years never tried, and you get sort of stranded for a few hours or days. But in the end you get it working and voila - you're an expert on the matter at hand :).