I can reproduce this very consistently. I have verified my 4.7.3 install and am using Windows 8.1 with a hefty graphics card. The bug report is below – thanks!
Access violation - code c0000005 (first/second chance not available)
UE4Editor_Engine!ConvertToMultilineToolTip() + 128 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\engine\private\materials\materialexpressions.cpp:188]
UE4Editor_Engine!UMaterialExpressionMaterialFunctionCall::GetConnectorToolTip() + 653 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\engine\private\materials\materialexpressions.cpp:6810]
UE4Editor_UnrealEd!UMaterialGraphNode::GetPinHoverText() + 366 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\editor\unrealed\private\materialgraphnode.cpp:654]
UE4Editor_GraphEditor!SGraphPin::GetTooltip() + 211 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\editor\grapheditor\private\sgraphpin.cpp:976]
UE4Editor_GraphEditor!TMemberFunctionCaller<SGraphPin,FText (__cdecl SGraphPin::*)(void)const __ptr64>::operator()<>() + 48 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\public\delegates\delegateinstanceinterface_variadics.h:161]
UE4Editor_GraphEditor!TTupleImpl<TIntegerSequence<> >::ApplyAfter_ExplicitReturnType<FText,TMemberFunctionCaller<SGraphPin,FText (__cdecl SGraphPin::*)(void)const __ptr64> >() + 25 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\public\delegates\tuple.h:113]
UE4Editor_GraphEditor!TBaseSPMethodDelegateInstance<1,SGraphPin,0,FText __cdecl(void)>::Execute() + 89 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:282]
UE4Editor_Slate!TBaseDelegate<FText>::Execute() + 26 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\public\delegates\delegatesignatureimpl_variadics.inl:439]
UE4Editor_Slate!TAttribute<FText>::Get() + 56 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\public\misc\attribute.h:135]
UE4Editor_Slate!SToolTip::IsEmpty() + 34 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\slate\private\widgets\stooltip.cpp:84]
UE4Editor_Slate!FSlateApplication::UpdateToolTip() + 644 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:2663]
UE4Editor_Slate!FSlateApplication::ProcessMouseMoveEvent() + 100 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4179]
UE4Editor_Slate!FSlateApplication::OnMouseMove() + 580 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4145]
UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() + 2984 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\private\windows\windowsapplication.cpp:1420]
UE4Editor_Core!FWindowsApplication::DeferMessage() + 318 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\private\windows\windowsapplication.cpp:1669]
UE4Editor_Core!FWindowsApplication::ProcessMessage() + 4016 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\private\windows\windowsapplication.cpp:742]
UE4Editor_Core!FWindowsApplication::AppWndProc() + 114 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\private\windows\windowsapplication.cpp:604]
user32 + 9268 bytes
user32 + 8855 bytes
UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() + 118 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:774]
UE4Editor!FEngineLoop::Tick() + 3737 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\launch\private\launchengineloop.cpp:2233]
UE4Editor!GuardedMain() + 1404 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\launch\private\launch.cpp:142]
UE4Editor!GuardedMainWrapper() + 26 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor!WinMain() + 249 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.7\engine\source\runtime\launch\private\windows\launchwindows.cpp:202]
UE4Editor!__tmainCRTStartup() + 329 bytes [f:\dd\vctools\crt\crtw32\dllstuff\crtexe.c:618]