Odd Favicon appearing in Google Apps

Favicon for Google Apps MailSomething odd has happened to my Google Apps favicon. It is no longer the familiar Gmail envelope but some gear and spanner (wrench) combination. The image above shows the new and old icons and you can see the new icon better below.

This has only appeared in the last week and only seems to affect Google Apps mail and not Gmail itself, as you can see from above.

A quick search online shows that others are seeing this too with all sorts of speculation as to what it could be. Myself I think it is simply a mistake – what do you think?