Negative or Inverted Colors

[Yopachi]

I've been using Antonio Villena's "VGA to Composite/S-Video adapter"
It works pretty flawlessly on my consumer 2001 32'' CRT. In a few cores the colors invert! When I mess with the scandoubler fx I get the correct colors back for a moment and then the image slowly fills in with negative colors. The cores affected:

Mario Bros. Arcade
Missile Command
Sega 32X
Minimig

to name a few

[MiSTer]
forced_scandoubler=0
ypbpr=0
composite_sync=1
vga_scaler=0
vscale_mode=0
vscale_border=0
hdmi_limited=0
direct_video=0
vga_sog=0
vsync_adjust=2
refresh_min=60
refresh_max=60

[Electron Junkie]

Guess I am not the only one that has run into this. Using an old JVC 27" with S-VHS.
I can confirm that 32X does this as well as a few arcade games (POW "Prisoners or War" comes to mind) though I haven't started keeping a list.

Am interested if its a signal strength issue.