This is really weird.
As I write Fantasy, there will naturally be made up names in my WIP. I don't add them to the dictionary (simple because I can't be bothered). Hence my typical page has a lot of red lines in it (and occasionally green). I'm not even at 60K, but when I opened it today, I got a message from Word that more or less says:
This document has too many spelling and/or grammar mistakes.
So, while I was staring stupendously at this message, the program crashed and shut down.
When I opened it again, it worked fine with no errors. Nevertheless, I added the character names to the dictionary as that should dramatically decreased Word's 'spelling error' count.
Weird. I've never heard of such a thing happening and it hasn't happened since. It's not exactly tech help so I put it in the Fantasy section.
And I don't use a lot of new names.