G'day there People,

Further to this strange confusion, I've discovered that when I
have protection on, and check the cell formatting, the Alignment tab of
the Format Cells dialogue shows a greyed out checkmark for the Merge
Cells Text Control. I've no idea whether that's significant or not, but
it's the only difference I detect between these and cells from sheets
that don't display this problem.

Still working on it,
Ken McLennan
Qld, Australia