Using Start Players as Spectators checkbox does not affect Player0

When setting up a custom game mode blueprint, if the "Start Players as Spectators" checkbox is checked the first player loaded in PIE will not be in spectator mode.

1. Open UE4 Editor (BP First Person Template)
2. Create new blueprint based on Game Mode (NewGameBP)
3. Open NewGameBP
4. In Details panel, check the box for "Start Players as Spectators"
5. Compile and save blueprint
6. In the main veiwport open World settings
7. Set GameMode Override to NewGameBP
8. PIE with 2 players

Result:
The second player will be in spectator mode but first player will be a spawned player.