Styles: Errors and Problems

In 7.1, when trying to delete a style I get the following error:

" is not a valid date

Actually, it happens with

Actually, it happens with other operations too. Sometimes, rebuilding seems to fix it and sometimes not.

I cannot reproduce this.

I cannot reproduce this. Please let me know more about your windows. Is it an English Windows?

English, yes. It is

English, yes. It is intermittent. If I see it again, I shall try to note the steps.

Maybe it was to do with the Reference Types that I was experimenting with?