Comment 17 for bug 480220

I looked some more at this, and relized some things:

When I run "xrandr --output TV1 --set mode" (I have tried with both PAL and NTSC-M here) it does not set a display mode fitting for the new output mode, and stays with the old.
i.e. switching to PAL I still have 0x44 as display mode, which seems to be 1024x768 for NTSC-m, and glxgears still work.
Switching to 0x106 (which seem to be 1024x768 for PAL) breaks glxgears.
Switching back to NTSC-M and glxgears is broken until I set 0x44.

So with other words glx seems broken for all PAL display modes my computer allows me to try(0x106-0x109), and works with all NTSC-M display modes (0x44-0x47).

Also every time xrandr fails to set a displaymode when switching between PAL and NTSC-M I get this message (i.e. "xrandr --output TV --set mode PAL && xrandr --output TV --set mode NTSC-M" shows this error one time, while "xrandr --output TV --set mode PAL && xrandr --output TV1 --mode 1024x768 && xrandr --output TV --set mode NTSC-M" shows it twice):

X Error of failed request: BadMatch (invalid parameter attributes)
  Major opcode of failed request: 147 (RANDR)
  Minor opcode of failed request: 21 (RRSetCrtcConfig)
  Serial number of failed request: 45
  Current serial number in output stream: 45