The question Does doing mathematics make you more intelligent? was closed, but 13 minutes after closing there was an answer posted.
I suppose this is a bug, and not a feature of the software.
I think it might be intended behavior. I remembered that there was a similar occurrence on MO; this meta.SO post is where Andrew Stacey filed the resulting bug report. Apparently the resolution was that
I can imagine that 13 minutes would qualify. However, I would have thought that, now that SE pages are almost-real-time updating with comments, answers, votes, etc. that the above answer would be out of date and that closure would take effect immediately, without someone having to reload the page.