(KVO) Crash on exit

[MaddTheSane]

There's a crash on exit due to Key-value observing not being happy:

2021-04-05 12:35:41.568218-0600 Boxer[13480:13258843] [General] Cannot remove an observer <NSKeyValueObservance 0x600001ac4870> for the key path "currentFrame.scaledResolution" from <BXMetalRenderingView 0x12a990600>, most likely because the value for the key "currentFrame" has changed without an appropriate KVO notification being sent. Check the KVO-compliance of the BXMetalRenderingView class.
2021-04-05 12:35:41.573053-0600 Boxer[13480:13258843] [General] (
	0   CoreFoundation                      0x000000019c39a320 __exceptionPreprocess + 240
	1   libobjc.A.dylib                     0x000000019c0c8c04 objc_exception_throw + 60
	2   Foundation                          0x000000019d0c8aa4 -[NSKeyValueNestedProperty object:didRemoveObservance:recurse:] + 672
	3   Foundation                          0x000000019d0975a8 -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:] + 284
	4   Foundation                          0x000000019d097434 -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:] + 88
	5   Foundation                          0x000000019d0c893c -[NSKeyValueNestedProperty object:didRemoveObservance:recurse:] + 312
	6   Foundation                          0x000000019d097bc4 -[NSKeyValueUnnestedProperty object:didRemoveObservance:recurse:] + 204
	7   Foundation                          0x000000019d0975a8 -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:] + 284
	8   Foundation                          0x000000019d097434 -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:] + 88
	9   AppKit                              0x000000019ec7e230 -[NSAutounbinder removeObserver:forKeyPath:] + 204
	10  AppKit                              0x000000019eadbb8c -[NSBinder _updateObservingRegistration:] + 600
	11  AppKit                              0x000000019eb84aa0 -[NSBinder breakConnection] + 112
	12  AppKit                              0x000000019eb84794 -[NSObject(NSKeyValueBindingCreation) unbind:] + 192
	13  AppKit                              0x000000019ec89ec4 -[NSAutounbinder retainBindingTargetAndUnbind] + 148
	14  AppKit                              0x000000019ecc7268 -[NSWindowController release] + 100
	15  Foundation                          0x000000019d1fb84c empty + 76
	16  Foundation                          0x000000019d095650 dealloc + 52
	17  Foundation                          0x000000019d0955c0 -[NSConcreteMapTable dealloc] + 68
	18  AppKit                              0x000000019f1973bc ___NSTouchBarFinderSetNeedsUpdateOnMain_block_invoke_2 + 1764
	19  AppKit                              0x000000019ebc99a0 NSDisplayCycleObserverInvoke + 188
	20  AppKit                              0x000000019ebc951c NSDisplayCycleFlush + 832
	21  QuartzCore                          0x00000001a25a1aa0 _ZN2CA11Transaction19run_commit_handlersE18CATransactionPhase + 120
	22  QuartzCore                          0x00000001a25a08e8 _ZN2CA11Transaction6commitEv + 332
	23  AppKit                              0x000000019ec72c88 __62+[CATransaction(NSCATransaction) NS_setFlushesWithDisplayLink]_block_invoke + 304
	24  AppKit                              0x000000019f3c5c6c ___NSRunLoopObserverCreateWithHandler_block_invoke + 64
	25  CoreFoundation                      0x000000019c31be08 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 36
	26  CoreFoundation                      0x000000019c31bc54 __CFRunLoopDoObservers + 576
	27  CoreFoundation                      0x000000019c31b1ac __CFRunLoopRun + 768
	28  CoreFoundation                      0x000000019c31a740 CFRunLoopRunSpecific + 600
	29  HIToolbox                           0x00000001a3e3f5c4 RunCurrentEventLoopInMode + 292
	30  HIToolbox                           0x00000001a3e3f284 ReceiveNextEventCommon + 320
	31  HIToolbox                           0x00000001a3e3f124 _BlockUntilNextEventMatchingListInModeWithFilter + 76
	32  AppKit                              0x000000019eaf482c _DPSNextEvent + 868
	33  AppKit                              0x000000019eaf31ac -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1312
	34  AppKit                              0x000000019eae5060 -[NSApplication run] + 600
	35  AppKit                              0x000000019eab6804 NSApplicationMain + 1064
	36  Boxer                               0x0000000100a539f8 main + 40
	37  libdyld.dylib                       0x000000019c23df34 start + 4
)

[MaddTheSane]

Typing EXIT in the DOS prompt doesn't cause the crash.