You can't get Merged Cells to obey *anything*
Seriously, merged cells arguably are the most abominable "feature" ever
written into the program. Anyone [except MS

] would recommend that you
avoid them like the plague... At least in any working Excel file. If you
want to create a Form to be printed for hand-written or typed data
collection you may be able to get away with them, but other than that they
will -- invariably -- cause any degree of interference & problems...
Possibly resulting in corruption to the point that the file becomes
unusable.
Regards |:>)
Bob Jones
[MVP] Office:Mac