Can't add accidentals in Note Mode

It's reported and a fix is being discussed among the programmers along with a couple of other issues with the new note input mode concerning accidentals.

BTW, you can enter accidentals while in note entry mode, you now have to enter the accidental then the note. This allows you to hear the correct note entered. A known problem is that if the note is in the wrong octave with a courtesy accidental, the accidental will be removed when you move it with ctrl+arrow and you will either have to use the palette or go back after exiting note entry mode to fix it.

To be clear though, the change to have the accidental buttons apply to the next note instead of the previous note is deliberate, it makes them more consistent with the other toolbar buttons that also affect the next note (duration, rest, voice, etc). You can still add accidentals after entering a note using the keybaord shortcuts up/down or using the palette. There are some subtle details of the interactions still be tweaked, to be sure, but it's important to realize it does basically work now, you just need to adjust to the new more consistent behavior.