One of my students just showed me the following strange behaviour with Maple 18 (17?) on her Mac computer:
After entering anything at all in math mode, the Enter key has no effect.
After an empty line in math mode the Enter key works fine, and also after anything (including nothing) in text mode.
She has uninstalled and reinstalled Maple several times.
I have absolutely no clue. Do you?
If nobody has a clue, I will be back with more detailed information.