Yes, I did confirm it with an Excel 2003 workbook.

No, I wouldn't have expected textbox change subs to fire. The text boxes
wouldn't be linked to the second sheet. The combo boxes ARE linked to the
second sheet, and therefore are firing when that second sheet is changed in
some particular ways.

No idea why the supposedly unassociated cell moves trigger this, but they
do, and have over several levels of Excel.