Any of Blargg's NTSC filters causes left side to wrap around onto the right

[emilyst]

For reference, I'm using RetroArch 1.10.1 built for tvOS using Xcode 13.2.1 (13C100) on macOS 12.2.1 (21D62), with Genesis Plus GX Wide built from commit fa71a1640f6a01025a045b616007c2fe4effd384 from http://buildbot.libretro.com/nightly/apple/tvos-arm64/latest/genesis_plus_gx_wide_libretro_tvos.dylib.zip.

Discovered an unexpected interaction when using any of Blargg's NTSC filters (available in the core video options). It causes widescreen games to draw the left side of the screen a second time on the right side, overlapping the widescreen content.

I found this happened in any Sega Genesis game I tried. It also happened regardless of the particular NTSC filter I used.

It resolved if I disabled the NTSC filter. Changing other video options (like the interlaced mode 2 output option, or enabling shaders) had no effect.

Example with NTSC filter enabled (using a CRT shader):

Example with NTSC filter disabled (using a CRT shader):

For the time being, I can workaround by disabling the NTSC filter, so this is not an urgent issue.