Every time I time I open a THEMED window for submissions, I am inundated with submissions that have nothing to do with the theme.
I don't expect the submissions to all be very overtly about a stated theme, but when I ask for a "fairy godmother" submission, and I get a high fantasy tale about warring gnomes, I get annoyed. Very.
I have to read all the submissions the whole way through, just in case something theme related happens by the end. As you all know, I am a one-person show. A few off-topic submissions really slow me down.
Sometimes I ask people why they submit off topic. I'm often told something like: I thought it was so good, you'd publish anyway.
This is a PG site, so I won't say what my gut reaction is to that kind of absurd display of ego and desperation.
Writers need to believe me when I tell you that editors in general expect you to follow the rules. Don't kid yourself that your work is trailing clouds of genius and is therefore irresistible. Resisting off-theme working is very easy.
Thus endeth the lecture.
But do know that the competition is fierce, and I always find excellent work by people who follow the theme. The fairy godmother issue is no different.