I searched questions tagged c++, and I obtained the following results (look at first question):
Refreshing the page a little bit later left the question out of results, so it looks like a race condition issue.
No repro on my end.
Buuuuuuuut it might be a simple caching issue (I mean, if it is an issue at all), the question was tagged with c++.
There is always a lag when the tags on a question are edited before the new tags are reflected in searches. This is easy to test yourself and I see it all the time when retagging.
Not a bug, just caching.
Edit: I just removed python from a question, and it showed up in the search results for maybe three minutes before disappearing.