>Yes they are all based on cursors.

Then, if you reselect records into a cursor which is used as Combo.Rowsource, you should:
Combo.Rowsource=""
Select .... Into Cursor tmp
Combo.Rowsource="tmp"
Usually, lack of this precaution will invoke error message 'Cannot Access Selected Work Area ...'. The same is applied for grids. It's interesting that they don't produce error messages, but turn to empty.