@BR: my apologies for sounding testy. Life is a bit complicated here ...
Clearly there is something wrong given that several people have seen the problem. My problem is that I can't repeat it so I have no idea where to look. I have tried creating a new column, hiding and restoring a column, and sitting for 5 minutes chanting "ooomm", all without a failure. Eating a bowl of ice cream didn't work either.
If your tests come up with something repeatable then I will be happy to look at it and (I hope) fix it. Or even if things aren't repeatable but provide enough pointers for where to look.