Describe the bug
When calling CompositorBringToFront followed by CompositorGoToBack, the compositor freezes, no frames advance, the headset has a stuck frame, and vrmonitor shows no frames pumping in the performance graph.

To Reproduce
Steps to reproduce the behavior:

1. Call those two functions in succession from a background session that does nothing else.

Expected behavior
Nothing, since this is a direct-mode system.

System Information (please complete the following information):

• Steam client version (build number or date): 1785347151
• SteamVR version: 2.17.6
• Distribution (e.g. Ubuntu): Arch Linux
• Steam runtime diagnostics: runtime diagnostics.txt
• Steam and SteamVR logs: steam-logs.tar.gz
• Minidumps: steam-minidumps.tar.gz