When she kissed him for the first time?
She thought that she is him right?
but to be honest Rogue didn't used her powers sucesfully in early / mid 90s even once. She kissed Magneto and did nothing to him. She touched this strange rubber mutant to suffer. She touched Gambit 2 times and both times she was affected strongly.
remydat :
Rogue should know because she absorbed powers of all Avengers and Xmen during Uncanny Avengers vol 1. She lost control then.No the point that matters is the fact they were alone so Rogue shouldn't know.
She was hearing their voices which means that she absorbed not only powers but also psyche of all these characters.