I had a number of achievements I was working on and had already received partial credit for:
Pink'd - Up to Ghom
Jars of Destruction - 600+
Savior - ~20
and a number of others
I can't be certain exactly when the presumed error occurred, but they're all back at 0 or unchecked respectively. At the beginning of my gaming session I was 59, I hit 60 and continued to plod about; downed from Ghom to Siegebreaker.
When I checked my progression around Midnight, before signing off, was when I realized they had been reset. I figured it might be something to do with hitting 60, perhaps it's not a bug?
I don't need the achieve credits refunded, they're easy to get back over time, but I thought you might want a heads-up.