I was in the process of trying to replicate this and missed a step so I tried to close UE4 and got the following crash…
Fatal error!
Address = 0xc3e03a00 (filename not found)
IncrementalPurgeGarbage() 0x4e7c332f + 0 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\coreuobject\private\uobject\garbagecollection.cpp:972] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-CoreUObject.dll]
CollectGarbage() 0x4e7990a5 + 0 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\coreuobject\private\uobject\garbagecollection.cpp:1171] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-CoreUObject.dll]
FEditorFileUtils::SaveDirtyPackages() 0x3d8a51fa + 0 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\editor\unrealed\private\filehelpers.cpp:2363] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
FMainFrameHandler::CanCloseEditor() 0x39e0e00a + 37 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\editor\mainframe\private\frame\mainframehandler.h:207] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-MainFrame.dll]
FMainFrameHandler::CloseRootWindowOverride() 0x39e0fb6e + 5 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\editor\mainframe\private\frame\mainframehandler.h:226] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-MainFrame.dll]
SWindow::RequestDestroyWindow() 0x4b6d1cdc + 31 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\slatecore\private\widgets\swindow.cpp:965] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-SlateCore.dll]
SWindowTitleBar::CloseButton_OnClicked() 0x47709815 + 0 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\slate\private\framework\application\swindowtitlebar.h:400] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Slate.dll]
TBaseSPMethodDelegateInstance_RetVal_NoParams::Execute() 0x4771baec + 17 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\core\public\delegates\delegateinstancesimpl.inl:161] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Slate.dll]
TBaseDelegate_RetVal_NoParams::Execute() 0x47956f7a + 6 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\core\public\delegates\delegatesignatureimpl.inl:1058] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Slate.dll]
SButton::OnMouseButtonUp() 0x47998f59 + 17 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\slate\private\widgets\input\sbutton.cpp:188] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Slate.dll]
FSlateApplication::ProcessMouseButtonUpEvent() 0x47764cff + 20 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:3421] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Slate.dll]
FSlateApplication::OnMouseUp() 0x47752219 + 17 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:3388] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Slate.dll]
FWindowsApplication::ProcessDeferredMessage() 0x4bad6f65 + 12 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\core\private\windows\windowsapplication.cpp:1345] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FWindowsApplication::DeferMessage() 0x4bac1821 + 74 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\core\private\windows\windowsapplication.cpp:1636] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FWindowsApplication::ProcessMessage() 0x4bad80ae + 41 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\core\private\windows\windowsapplication.cpp:736] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FWindowsApplication::AppWndProc() 0x4babd7e2 + 0 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\core\private\windows\windowsapplication.cpp:598] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
Address = 0x65052434 (filename not found) [in C:\WINDOWS\system32\USER32.dll]
Address = 0x65052297 (filename not found) [in C:\WINDOWS\system32\USER32.dll]
FWindowsPlatformMisc::PumpMessages() 0x4bad8556 + 48 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:761] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FEngineLoop::Tick() 0x191673ad + 8 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\launch\private\launchengineloop.cpp:2080] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor.exe]
GuardedMain() 0x1915cc7c + 0 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\launch\private\launch.cpp:133] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor.exe]
GuardedMainWrapper() 0x1915ccea + 5 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\launch\private\windows\launchwindows.cpp:125] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor.exe]
WinMain() 0x19168ad9 + 17 bytes [File=e:\source\unrealengine-4.4.0-release\engine\source\runtime\launch\private\windows\launchwindows.cpp:201] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor.exe]
__tmainCRTStartup() 0x19169989 + 21 bytes [File=f:\dd\vctools\crt\crtw32\dllstuff\crtexe.c:618] [in E:\Source\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor.exe]
Address = 0x62ec16ad (filename not found) [in C:\WINDOWS\system32\KERNEL32.DLL]
Address = 0x653134a5 (filename not found) [in C:\WINDOWS\SYSTEM32\ntdll.dll]
Address = 0x653134a5 (filename not found) [in C:\WINDOWS\SYSTEM32\ntdll.dll]