Crash when trying to change game mode settings

Trying to change game mode settings after restarting the editor will cause the editor to crash.

1. Create new empty project
2. Create a Game Mode blueprint (CustomGameModeBP)
3. Open world settings and set GameMode Override to CustomGameModeBP
4. File->Save All
5. Close and reopen the editor
6. If it doesn't load immediately, reload saved level
7. Open world settings
8. Expand Selected GameMode
9. Click on drop down box for Default Pawn Class

Result:
Editor will crash without crash reporter

Expected:
Change the Game Mode settings after opening a project