Not a regression as it occurs in 4.14.3
Result: Selecting anything else in the viewport multi selects like the Ctrl key is held down (Can be seen in the world outliner). Eventually a crash may occur after multiple clicks and pressing the delete button. Crash 3 out of 5 times.
UE4Editor_Core!FDebug::AssertFailed() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:349] UE4Editor_UnrealEd!UUnrealEdEngine::edactDeleteSelected() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\unrealed\private\editoractor.cpp:690] UE4Editor_UnrealEd!UUnrealEdEngine::Exec_Actor() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\unrealed\private\unrealedsrv.cpp:2530] UE4Editor_UnrealEd!UUnrealEdEngine::Exec() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\unrealed\private\unrealedsrv.cpp:727] UE4Editor_UnrealEd!UEditorEngine::Exec() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\unrealed\private\editorserver.cpp:5631] UE4Editor_UnrealEd!UUnrealEdEngine::Exec() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\unrealed\private\unrealedsrv.cpp:670] UE4Editor_LevelEditor!FLevelEditorActionCallbacks::ExecuteExecCommand() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\leveleditor\private\leveleditoractions.cpp:1648] UE4Editor_LevelEditor!TBaseStaticDelegateInstance<void __cdecl(void),FString>::ExecuteIfSafe() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:1027] UE4Editor_Slate!FUICommandList::ConditionalProcessCommandBindings() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\slate\private\framework\commands\uicommandlist.cpp:216] UE4Editor_Slate!FUICommandList::ProcessCommandBindings() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\slate\private\framework\commands\uicommandlist.cpp:160] UE4Editor_UnrealEd!SEditorViewport::OnKeyDown() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\unrealed\private\seditorviewport.cpp:109] UE4Editor_LevelEditor!SLevelViewport::OnKeyDown() [d:\build\++ue4+release-4.15+compile\sync\engine\source\editor\leveleditor\private\slevelviewport.cpp:444] UE4Editor_Slate!<lambda_2afcd964c763e269e2d1a63f3a72f846>::operator()() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4678] UE4Editor_Slate!FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FKeyEvent,<lambda_2afcd964c763e269e2d1a63f3a72f846> >() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:238] UE4Editor_Slate!FEventRouter::RouteAlongFocusPath<FEventRouter::FBubblePolicy,<lambda_2afcd964c763e269e2d1a63f3a72f846>,FKeyEvent>() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:220] UE4Editor_Slate!FSlateApplication::ProcessKeyDownEvent() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4676] UE4Editor_Slate!FSlateApplication::OnKeyDown() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4589] UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:1533] UE4Editor_Core!FWindowsApplication::DeferMessage() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:2120] UE4Editor_Core!FWindowsApplication::ProcessMessage() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:867] UE4Editor_Core!FWindowsApplication::AppWndProc() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:714] user32 user32 UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:980] UE4Editor!FEngineLoop::Tick() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\launch\private\launchengineloop.cpp:2977] UE4Editor!GuardedMain() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\launch\private\launch.cpp:166] UE4Editor!GuardedMainWrapper() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:134] UE4Editor!WinMain() [d:\build\++ue4+release-4.15+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:210] UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:264] kernel32 ntdll
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-41416 in the post.