It seems rather odd to me that when you use the shortcut for Enter unison above, you get a note consistent with the key signature and the note you are adding it to is ignored. For example, I have an E-flat in a score in the key of G (1 sharp). I pressed alt+1 and an E-natural was added.
I realize this is consistent with what happens in other situations when the interval is greater than a unison. I'm used to that and adjust the notes as necessary automatically to assure any accidentals are accounted for. It seems that entering a unison should actually produce a unison.