# An answer posted 30 seconds after the question was closed; how is it possible?

This question -- SVD for PCA: Why would one standardize the data matrix? -- was closed as a duplicate at 16:59:24 (nine minutes after having been posted). I can swear I saw it closed and without answers (that is when I wrote my comment). But then at 17:00:02 an answer was posted.

Answers cannot be posted to closed questions. So this is clearly due to some glitch or a loophole that allowed posting an answer within very short time after the question closure. I remember discussing a similar case in chat some time ago and one of the mods said that indeed it can happen.

I am curious what exactly the glitch/loophole is, and whether it is a bug or by design.

(Is it that if somebody opened the question page before the Q is closed and so can access the answer form, then they will be able to post an answer? So the SE software does not check if the Q is closed when receiving an A? Or it does check, but intentionally allows some leeway? Or is this leeway an unintentional consequence of some database updates taking time to propagate? Etc.)

There's a grace period after closure where an answer can still be accepted (however the Post Your Answer button becomes disabled, so you have to be clever enough to find a way around that).