Internet Explorer 8
Windows 7 : 64 bit
If I create a combo box where "allow blank" is false, a blank entry is not available in the drop-down selection (as expected). However, if I type quickly enough, I can blank out text, tab out of cell, and the cell would be blank.
I was expecting that the combo box would revert back to the previous value. Especially since "Force Selection" is also true. Blank is not a selection, so it cannot be a "forced" selection (it isn't any selection).
In provided test code, select a value. Then do a select all of the text and do "delete" and then "tab" as quickly as possible. The combo box will be left w/out a selection.