The core issue was that the BP editor was performing deactivation/cleanup work whenever any system asked if it can be closed, whereas other editors were not and sometimes interrupting/canceling the closure process. This led to situations where a BP editor tab deactivated itself before a different editor tab halted the window closing process, putting it in a dysfunctional state.
#jira UE-106350
#rb michael.noland matt.kuhlenschmidt
[CL 16391884 by justin hare in ue5-main branch]