This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
Use Single Process settings adjusted while Use Single Process is disable are retained while Use Single Process is enabled. This can be problematic when there are issues with having Use Single Process disabled, such as that found in [Link Removed]
Reproduced in 4.7.6, 4.8.1, and Main (//depot/UE4/Promotable-CL-2605171)
1. Open any project
2. Disable Use Single Process in Editor Preferences > Play
3. Switch Editor Multiplayer Mode to Play As Listen Server
4. PIE in Standalone with 2 players
5. Re-enable Use Single Process
6. PIE in Standalone with 2 players
Two Standalone windows are opened
One Standalone window is opened
Head over to the existing Questions & Answers thread and let us know what's up.