Previously verified site slipped back to pending verification

One of our sites which was verified and has been working since the
start of sitemaps changed back to the "pending verification" status. It
was only after a bit of digging about that I noticed the file name of
the verification file had changed from the previously stated,

GOOGLE40x8f7920c03fb78.html format to a lowercase google format of
google40x8f7920c03fb78.html

I renamed the file and re-verified and all is fine again.

What's that all about?

Has anyone else experienced this?

Perhaps Google need to think about some sort of alert to email
webmasters when status changes?