Not sure if anyone else has this issue or if it has been resolved before but after cut-scenes the scale of Sexymap shrinks in size and it will fix after a /reload.

I just tested this with the transition from Aggramar to Argus on LFR which plays both a cinematic and a movie, I could not reproduce this issue.

Have you tested this with only SexyMap enabled?

Seems to be an issue with SpartanUI, because it doesn't occur outside of it. Sorry for taking up your time.