I've noticed that most standard spell checker dictionaries don't seem to include the word "movies", although they do know the singular form, "movie". I've seen it in the Chrome web browser, and in two different keyboards on my Android phone, too. I'm fairly sure it isn't in the MS Office spell checker, though I haven't tested that theory on a new installation.
Did someone just forget to include it in some standard dictionary list, and now everyone is blindly reusing it?
Mokalus of Borg
PS - That's all, really.
PPS - Try it on your phone, word processor and web browser and let me know.