An addendum to my comment above: Three days later I have now also been bitten by Google's April Fool's feature/bug!
Today I received an email from someone asking why I was not replying to the other email thread started on April 1st. The person had clicked the 'drop the mic' button, and was not seeing any further replies to that thread. Not good!
I think it was a great, if risky, marketing move — people all over the internet are talking about Gmail today.
Sure, some may have had a bit of trouble, but the Gmail team apologized publicly, thus providing a finger-pointing target for stressed office workers.