I have seen this happen as well and am not sure what causes it exactly, but
it tends to happen (to me) when I receive a document from abroad (usually
France) and found that the Ruler untis are still denoted as Centimetre but
displays Points.
It does not seem to be an indicator of any corruption, so don't worry about
that.
The only way to reset is to save, close Word and reopen Word, back to cm's
until the next document lands in my Inbox ;-)
All the best
DeanH