Bug: changing pitch on percussion staff crashes MuseScore

Windows 7 Ultimate 64 bit OS
The attached file was working normally prior to the latest master updates. It is dated 12th of April, and it has not been changed since then.

When you open the file in the latest master it looks wrong, but I don't know if these are bugs or part of the new layout functionality: The first page of Kick staff looks wrong. It also adds an extra page after the title and before the first system. This score was only two pages previously.

Steps to reproduce crash: Open this file. Select the last note in the Hi-hat staff (very end of the file). Press the "N" key on your keyboard for Note Entry. It crashes in staff.cpp here:
https://github.com/musescore/MuseScore/blob/master/libmscore/staff.cpp#…
The call stack is:

0	Ms::Staff::mag	staff.cpp	696	0x7c04bc	
1	Ms::Chord::layoutPitched	chord.cpp	1707	0x8102db	
2	Ms::Chord::layout	chord.cpp	1679	0x810141	
3	Ms::Palette::paintEvent	palette.cpp	843	0x4a91d0	

In attempting to reproduce it again to provide the exact line of code that crashes, I just crashed it again, but a different error. This time I selected the first note in the Hi-hat staff and used my up and down arrow keys to change the pitch. The debugger ran very slowly, and the screen looked very strange for a while. Then I re-selected the same first note in the Hi-hat staff and changed the pitch via the up/down arrows, MuseScore crashes here: https://github.com/musescore/MuseScore/blob/master/libmscore/element.h#….

In general running in the debugger is super slow. And the steps above are the simplest way to cause this crash, but I caused it with the up/down arrow keys (to change pitch up/down) as well as by pressing "N".