**Blender Version**
Broken: rB2fb9a50a4f74 (blender2.8 HEAD)
Worked: 2.79
**Short description of error**
Crash when toggling side bars (toolshelf / properties) while hovering button.
**Exact steps for others to reproduce the error**
* Mouse hover any property from the Properties panel of the viewport
* Toggle the panel visibility (N)
`SUMMARY: AddressSanitizer: heap-use-after-free //source/blender/windowmanager/intern/wm_event_system.c:1990 in wm_handler_operator_call`
Fullbacktrace: P695