Well, it's quite a common bug in distributed systems to have mismatching timestamps because different server machines which tagged different elements had different clock times.

Hopefully the time stamp of a post isn't done at the user machine level (or using data from it, such as stuff from HTTP headers) as those are far more likely to be misconfigured.

The only way I see for this be a Memmy bug is if there are two timestamp fields (a user one and a server one) and the user one is being picked up (I can only think of a separate user timestamp making sense for data manipulations on the user's own machine of the user's own posts).