I eventually opened a new file, and copied everything across into it. The new file behaved properly, and off I go.
I am not at all sure this is how it is supposed to work, and I would still want to avoid it if possible.
Just pasted some stuff in from a .csv sheet - the problem returned, so still no solution.
What am I doing wrong? Genuinely, this is making the program unuseable.
I went to the answer suggested, and agree that it might be a similar problem, but the problem arises on every move from one row to the next.
I tried the fix suggested but it did not work. I have also searched in the on-line manual with no indication returned.
Also this is happening:
not (noticeably) on loading, but on editing.
It seems to come and go - the only common factor seems to be on setting a font for the entire sheet.
I am using build Version: 126.96.36.199 (x64).