And here's the backtrace from breaking on the actual assertion:

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 10.5
  * frame #0: 0x00000001003f1cd0 libwx_osx_cocoau-3.0.0.dylib`wxOnAssert(char const*, int, char const*, char const*, char const*)
    frame #1: 0x0000000100538b83 libwx_osx_cocoau-3.0.0.dylib`wxWindow::MacPaintBorders(int, int) + 275
    frame #2: 0x0000000100539e57 libwx_osx_cocoau-3.0.0.dylib`wxWindow::MacPaintChildrenBorders() + 407
    frame #3: 0x00000001005f7aa2 libwx_osx_cocoau-3.0.0.dylib`wxWidgetCocoaImpl::drawRect(void*, NSView*, void*) + 1442
    frame #4: 0x00000001005f6236 libwx_osx_cocoau-3.0.0.dylib`wxOSX_drawRect(NSView*, objc_selector*, CGRect) + 86
    frame #5: 0x00007fff4746da6e AppKit`_NSViewDrawRect + 66
    frame #6: 0x00007fff474588b2 AppKit`-[NSView _drawRect:clip:] + 1752
    frame #7: 0x00007fff47457742 AppKit`-[NSView _recursiveDisplayAllDirtyWithLockFocus:visRect:] + 1425
    frame #8: 0x00007fff47457afa AppKit`-[NSView _recursiveDisplayAllDirtyWithLockFocus:visRect:] + 2377
    frame #9: 0x00007fff47455794 AppKit`-[NSView _recursiveDisplayRectIfNeededIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:topView:] + 908
    frame #10: 0x00007fff474553e2 AppKit`-[NSThemeFrame _recursiveDisplayRectIfNeededIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:topView:] + 65
    frame #11: 0x00007fff47452ce4 AppKit`-[NSView _oldDisplayRectIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:] + 1893
    frame #12: 0x00007fff4745231d AppKit`-[NSView _displayRectIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:] + 253
    frame #13: 0x00007fff4744ef0e AppKit`-[NSView displayIfNeeded] + 1302
    frame #14: 0x00007fff4744bc53 AppKit`-[NSWindow displayIfNeeded] + 280
    frame #15: 0x00007fff4744ba94 AppKit`__NSWindowGetDisplayCycleObserverForDisplay_block_invoke + 684
    frame #16: 0x00007fff47446b88 AppKit`NSDisplayCycleObserverInvoke + 162
    frame #17: 0x00007fff47446708 AppKit`NSDisplayCycleFlush + 1030
    frame #18: 0x00007fff54728ccb QuartzCore`CA::Transaction::run_commit_handlers(CATransactionPhase) + 49
    frame #19: 0x00007fff54728413 QuartzCore`CA::Transaction::commit() + 213
    frame #20: 0x00007fff474460a1 AppKit`__65+[CATransaction(NSCATransaction) NS_setFlushesWithDisplayRefresh]_block_invoke + 274
    frame #21: 0x00007fff49d29c94 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
    frame #22: 0x00007fff49d29bc9 CoreFoundation`__CFRunLoopDoObservers + 451
    frame #23: 0x00007fff49ccc74e CoreFoundation`__CFRunLoopRun + 1143
    frame #24: 0x00007fff49ccc085 CoreFoundation`CFRunLoopRunSpecific + 459
    frame #25: 0x00007fff48faa9db HIToolbox`RunCurrentEventLoopInMode + 292
    frame #26: 0x00007fff48faa61d HIToolbox`ReceiveNextEventCommon + 355
    frame #27: 0x00007fff48faa4a6 HIToolbox`_BlockUntilNextEventMatchingListInModeWithFilter + 64
    frame #28: 0x00007fff47344ffb AppKit`_DPSNextEvent + 965
    frame #29: 0x00007fff47343d93 AppKit`-[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1361
    frame #30: 0x00000001005da65c libwx_osx_cocoau-3.0.0.dylib`wxGUIEventLoop::OSXDoRun() + 220
    frame #31: 0x00000001004d5111 libwx_osx_cocoau-3.0.0.dylib`wxCFEventLoop::DoRun() + 49
    frame #32: 0x0000000100422b72 libwx_osx_cocoau-3.0.0.dylib`wxEventLoopBase::Run() + 162
    frame #33: 0x000000010bd56591 _eeschema.kiface`DIALOG_SHIM::ShowQuasiModal() + 673
    frame #34: 0x000000010b98eaaf _eeschema.kiface`SCH_EDIT_FRAME::EditComponentFieldText(SCH_FIELD*) + 735
    frame #35: 0x000000010bb50846 _eeschema.kiface`SCH_EDIT_FRAME::OnEditItem(wxCommandEvent&) + 982
    frame #36: 0x000000010050161f libwx_osx_cocoau-3.0.0.dylib`wxEventHashTable::HandleEvent(wxEvent&, wxEvtHandler*) + 239
    frame #37: 0x0000000100502941 libwx_osx_cocoau-3.0.0.dylib`wxEvtHandler::ProcessEvent(wxEvent&) + 209
    frame #38: 0x000000010bd7b678 _eeschema.kiface`EDA_BASE_FRAME::ProcessEvent(wxEvent&) + 152
    frame #39: 0x0000000100502aa1 libwx_osx_cocoau-3.0.0.dylib`wxEvtHandler::ProcessEventLocally(wxEvent&) + 161
    frame #40: 0x00000001005028d4 libwx_osx_cocoau-3.0.0.dylib`wxEvtHandler::ProcessEvent(wxEvent&) + 100
    frame #41: 0x000000010b9d3e26 _eeschema.kiface`SCH_EDIT_FRAME::OnHotKey(wxDC*, int, wxPoint const&, EDA_ITEM*) + 3974
    frame #42: 0x000000010b989882 _eeschema.kiface`SCH_EDIT_FRAME::GeneralControl(wxDC*, wxPoint const&, unsigned int) + 738
    frame #43: 0x000000010ba3940d _eeschema.kiface`SCH_DRAW_PANEL::OnKeyEvent(wxKeyEvent&) + 861
    frame #44: 0x0000000100502cb2 libwx_osx_cocoau-3.0.0.dylib`wxEvtHandler::SearchDynamicEventTable(wxEvent&) + 178
    frame #45: 0x0000000100502a3b libwx_osx_cocoau-3.0.0.dylib`wxEvtHandler::ProcessEventLocally(wxEvent&) + 59
    frame #46: 0x00000001005028d4 libwx_osx_cocoau-3.0.0.dylib`wxEvtHandler::ProcessEvent(wxEvent&) + 100
    frame #47: 0x0000000100738833 libwx_osx_cocoau-3.0.0.dylib`wxScrollHelperEvtHandler::ProcessEvent(wxEvent&) + 35
    frame #48: 0x0000000100502d5c libwx_osx_cocoau-3.0.0.dylib`wxEvtHandler::SafelyProcessEvent(wxEvent&) + 12
    frame #49: 0x000000010053b021 libwx_osx_cocoau-3.0.0.dylib`wxWindow::OSXHandleKeyEvent(wxKeyEvent&) + 273
    frame #50: 0x00000001005fa4d9 libwx_osx_cocoau-3.0.0.dylib`wxWidgetCocoaImpl::DoHandleCharEvent(NSEvent*, NSString*) + 249
    frame #51: 0x00000001005f6eab libwx_osx_cocoau-3.0.0.dylib`wxWidgetCocoaImpl::insertText(NSString*, NSView*, void*) + 315
    frame #52: 0x00007fff47667191 AppKit`-[NSTextInputContext(NSInputContext_WithCompletion) insertText:replacementRange:completionHandler:] + 169
    frame #53: 0x00007fff47d2ce78 AppKit`__55-[NSTextInputContext handleTSMEvent:completionHandler:]_block_invoke_2.309 + 102
    frame #54: 0x00007fff476670e2 AppKit`-[NSTextInputContext do_HandleTSMEvent_insertFixLenTextLoop:whileCondition:dispatchWorkEach:afterEachInsertText:continuation:] + 105
    frame #55: 0x00007fff47d2b05b AppKit`-[NSTextInputContext tryHandleTSMEvent_insertFixLenText_withContext:dispatchCondition:setupForDispatch:nestedWorkaroundCondition:nestedWorkaroundDispatchWork:loopCondition:dispatchWorkEach:afterEachInsertText:continuation:] + 308
    frame #56: 0x00007fff47d2c7e7 AppKit`__55-[NSTextInputContext handleTSMEvent:completionHandler:]_block_invoke.265 + 2976
    frame #57: 0x00007fff47666d4e AppKit`__55-[NSTextInputContext handleTSMEvent:completionHandler:]_block_invoke_2 + 74
    frame #58: 0x00007fff47666cd6 AppKit`-[NSTextInputContext tryHandleTSMEvent_HasMarkedText_withDispatchCondition:dispatchWork:continuation:] + 87
    frame #59: 0x00007fff476664ce AppKit`-[NSTextInputContext handleTSMEvent:completionHandler:] + 1749
    frame #60: 0x00007fff47665d81 AppKit`_NSTSMEventHandler + 306
    frame #61: 0x00007fff48fa8a6e HIToolbox`DispatchEventToHandlers(EventTargetRec*, OpaqueEventRef*, HandlerCallRec*) + 1422
    frame #62: 0x00007fff48fa7e1f HIToolbox`SendEventToEventTargetInternal(OpaqueEventRef*, OpaqueEventTargetRef*, HandlerCallRec*) + 371
    frame #63: 0x00007fff48fa7ca5 HIToolbox`SendEventToEventTargetWithOptions + 45
    frame #64: 0x00007fff4900f4df HIToolbox`SendTSMEvent_WithCompletionHandler + 383
    frame #65: 0x00007fff4900f94a HIToolbox`__SendUnicodeTextAEToUnicodeDoc_WithCompletionHandler_block_invoke + 387
    frame #66: 0x00007fff4900f7b8 HIToolbox`__SendFilterTextEvent_WithCompletionHandler_block_invoke + 221
    frame #67: 0x00007fff4900f52e HIToolbox`SendTSMEvent_WithCompletionHandler + 462
    frame #68: 0x00007fff4900f333 HIToolbox`SendFilterTextEvent_WithCompletionHandler + 225
    frame #69: 0x00007fff4900eff4 HIToolbox`SendUnicodeTextAEToUnicodeDoc_WithCompletionHandler + 280
    frame #70: 0x00007fff4900ed9e HIToolbox`__utDeliverTSMEvent_WithCompletionHandler_block_invoke_2 + 283
    frame #71: 0x00007fff4900ebfd HIToolbox`__utDeliverTSMEvent_WithCompletionHandler_block_invoke + 355
    frame #72: 0x00007fff4900ea1b HIToolbox`TSMKeyEvent_WithCompletionHandler + 598
    frame #73: 0x00007fff4900e7aa HIToolbox`__TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_4 + 250
    frame #74: 0x00007fff4900e5d9 HIToolbox`__TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_3 + 257
    frame #75: 0x00007fff4900e31e HIToolbox`__TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_2 + 282
    frame #76: 0x00007fff4900e082 HIToolbox`__TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke + 274
    frame #77: 0x00007fff4900d677 HIToolbox`TSMProcessRawKeyEventWithOptionsAndCompletionHandler + 3398
    frame #78: 0x00007fff47d31451 AppKit`__84-[NSTextInputContext _handleEvent:options:allowingSyntheticEvent:completionHandler:]_block_invoke_3.779 + 110
    frame #79: 0x00007fff47d30a4e AppKit`__204-[NSTextInputContext tryTSMProcessRawKeyEvent_orSubstitution:dispatchCondition:setupForDispatch:furtherCondition:doubleSpaceSubstitutionCondition:doubleSpaceSubstitutionWork:dispatchTSMWork:continuation:]_block_invoke.734 + 115
    frame #80: 0x00007fff47d3093f AppKit`-[NSTextInputContext tryTSMProcessRawKeyEvent_orSubstitution:dispatchCondition:setupForDispatch:furtherCondition:doubleSpaceSubstitutionCondition:doubleSpaceSubstitutionWork:dispatchTSMWork:continuation:] + 245
    frame #81: 0x00007fff47d3100a AppKit`-[NSTextInputContext _handleEvent:options:allowingSyntheticEvent:completionHandler:] + 1286
    frame #82: 0x00007fff47d307fe AppKit`-[NSTextInputContext _handleEvent:allowingSyntheticEvent:] + 107
    frame #83: 0x00007fff47664840 AppKit`-[NSView interpretKeyEvents:] + 209
    frame #84: 0x00000001005fa742 libwx_osx_cocoau-3.0.0.dylib`wxWidgetCocoaImpl::DoHandleKeyEvent(NSEvent*) + 466
    frame #85: 0x00000001005f6d1c libwx_osx_cocoau-3.0.0.dylib`wxWidgetCocoaImpl::keyEvent(NSEvent*, NSView*, void*) + 348
    frame #86: 0x00007fff474b1b9f AppKit`-[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 6840
    frame #87: 0x00007fff474afe9f AppKit`-[NSWindow(NSEventRouting) sendEvent:] + 478
    frame #88: 0x00000001005e4fab libwx_osx_cocoau-3.0.0.dylib`-[wxNSWindow sendEvent:] + 123
    frame #89: 0x00007fff47350101 AppKit`-[NSApplication(NSEvent) sendEvent:] + 2953
    frame #90: 0x0000000100510c12 libwx_osx_cocoau-3.0.0.dylib`-[wxNSApplication sendEvent:] + 98
    frame #91: 0x00007fff4733dee8 AppKit`-[NSApplication run] + 755
    frame #92: 0x00000001005da62e libwx_osx_cocoau-3.0.0.dylib`wxGUIEventLoop::OSXDoRun() + 174
    frame #93: 0x00000001004d5111 libwx_osx_cocoau-3.0.0.dylib`wxCFEventLoop::DoRun() + 49
    frame #94: 0x0000000100422b72 libwx_osx_cocoau-3.0.0.dylib`wxEventLoopBase::Run() + 162
    frame #95: 0x00000001003f1463 libwx_osx_cocoau-3.0.0.dylib`wxAppConsoleBase::MainLoop() + 99
    frame #96: 0x000000010057393a libwx_osx_cocoau-3.0.0.dylib`wxApp::OnRun() + 26
    frame #97: 0x000000010001fe78 kicad`APP_KICAD::OnRun() + 24
    frame #98: 0x000000010045c40a libwx_osx_cocoau-3.0.0.dylib`wxEntry(int&, wchar_t**) + 58
    frame #99: 0x000000010001cd96 kicad`main + 38
    frame #100: 0x00007fff761e53d5 libdyld.dylib`start + 1
    frame #101: 0x00007fff761e53d5 libdyld.dylib`start + 1