[AccessD] Puzzling Form hebaviour Access 2003

I'm working on an inherited app which contains one huge table with numerous
fields, distributed in groups across about 6 tabs. There are no subforms --
the whole form displays just one row -- 20 controls on the first tab page,
20 on the second, etc.

Whenever I move the mouse over the form, most or all of the controls on the
displayed tab page sort of jiggle or shimmer. They don't change values, and
it happens too quickly to think they are re-querying, but nevertheless it is
annoying. I've checked such event controls as keydown, onCurrent etc. and
nothing looks as if it's causing this annoying behaviour. Is it possibly
just because there are so many controls?

Incidentally, I plan to normalise this table and that may make this problem
of multiple nested tables inside one go away, but in the interim I'm
wondering about this.

Any clues where to look?

TIA,
Arthur