Tested in 0.9.6 stable under Windows XP

Steps:

1. Open (or create) a score with at least one key signature
2. Click on the key signature to select it
3. Save the score with the key signature selected and close it
4. Re-load the score

Result:
MuseScore crashes.

Expected result:
The score is loaded and displayed.

This issue is similar, but not identical, to this one.

Details:
The offending code line is:
system.h, 124: System::staff(int staffIdx)
called by
keysig.cpp, 70: KeySig::canvasPos()
apparently while clearing all selections during the loading process.
It seems like the KeySig::canvasPos() function is accessing the collection of systems before it is initialized (or created).

M.