note input doesn't account for clef changes

Reproduce:

First, myself and jeetee (freenode/#musescore) have not always been able to reproduce this bug. That said, it occurs often enough:

1. incorrect display, correct note/audio

   example-1.mscz

   How to reproduce:

   • start with a treble template in 4/4
   • drag the bass clef onto the first measure
   • insert four middle-c quarter notes
   • drag the treble clef to the second note

   The three "c" notes after the treble clef display as "a", even though they are correctly played as "c"

2. correct display, incorrect note/audio

   example-2.mscz

   This is an excerpt from a real example - the right hand is modified to accentuate the fact that incorrect notes are played. I didn't notice the problem until I tried changing the notes via the keyboard, so while I'm not quite sure exactly how to reproduce, you should still notice the problem if you try to change any notes following the treble-clef change.

   How to reproduce (roughly):

   • [bass clef] enter a quarter note, convert it to a triplet, enter the 1st three notes
   • [bass clef] enter an eighth note, convert it to a sixteenth-triplet, enter the 2nd three notes, dragged to the correct pitch via the mouse
   • [bass clef] copy the previous sixteenth triplet over the final eighth rest, and drag the notes to the correct pitch via the mouse

   How to notice the issue:

   • change any of the bass-staff notes after the treble-clef with the keyboard instead of the mouse. The incorrect note will be displayed.