Crash when resizing brackets

Steps:
1- Create a score with 2 or more instruments (e.g. 3 flutes);
2- Drag and drop a bracket to the first instrument;
3- Double click the bracket and extend it to the second instrument;
4- Release the mouse -> crash.
OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 3.0.0, revision: d3d0f87
Attached the log file from AddressSanitizer (used under Windows via Clang compilation): the bracket was deleted when the systems were deleted, and updategrips is trying to update the grips of the old (deleted) bracket. Unfortunately, a side effect of 55db679ec
Note that even before 55db679ec the behavior was strange: after releasing the mouse the bracket could not be updated by moving the grip point.