Setting the Framerate setting to "fullspeed" causes the screen to flicker

Using the latest build of Parallel (as of writing) while using the OpenGL video driver in the latest nightly build of RetroArch, the screen will flicker if the Framerate setting is set to fullspeed. The screen doesn't flicker when set to "original". This seems to affect any game that can run in Parallel. My Parallel settings have always remained the same, and this problem hasn't happened until just recently. I am not using any shaders. I 'reinstalled' retroarch by making a new folder and redownloading the same nightly builds and I can reproduce the same issue by setting the framerate setting to fullspeed.

You should be able to reproduce this issue by doing the following:
1.) Download the latest nightly build of Retroarch and Parallel (as of writing)
2.) Open Retroarch and make sure the video driver is set to 'gl'.
3.) Load up any game using the Parallel core (you shouldn't get any screen flickering.
4.) Press F1 and select 'Option'.
5.) Set the Framerate option to "fullspeed".
6.) Close the ROM out and reopen it within Retroarch, the game should now flicker. Restarting the game as recommended by the setting doesn't seem to apply the setting correctly (another bug?), but closing the ROM out and reopening it seems to.

My settings in Parallel are configured as follows, but I've also tested with default settings and setting the Framerate setting to fullspeed before closing/reopening the ROM seems to always cause the problem:
CPU Core - dynamic_recompiler
Audio Buffer Size - 2048
Analog Deadzone - 15
Player 1 Pak - rumble
Enable Expansion Pak RAM - ON
GFX Accuracy (restart) - verhigh
Send audio lists to HLE RSP - OFF
GFX Plugin - auto
RSP Plugin - auto
Resolution (restart) 2240x1680
Aspect ratio hint - widescreen
Texture Filtering - automatic
(Glide64) Polygon Offset Factor - -3.0
(Glide64) Polygon Offset Units - -3.0
(Angrylion) VI Overlay - OFF
VI Refresh (Overclock - 2200
Buffer Swap - OFF
Framerate (restart) - fullspeed

My computer:
OS - Windows 10 x64
Graphics - NVIDIA GeForce 680 GTX (388.71)
CPU - Intel 2500k
Motherboard - Asrock z68 gen3

EDIT: I've also tested this on macos and the same thing occurs as well.

Reproduce the flicker with the Parallel core in RetroArch using the OpenGL ('gl') video driver and the Framerate option set to 'fullspeed'; compare it with 'original'. Trace the handling of this option and its restart behavior, then verify that reopening a game applies the setting without flickering on the reported Windows and macOS cases.