Comment # 4 on bug 84944 from Michel Dänzer

Can you get the same or at least similar tearing on Brazos with

 Option "SwapbuffersWait" "off"

or

 Option "AccelMethod" "glamor"

in xorg.conf? If yes, the problem is that page flipping cannot be used for the
MythTV window, most likely because its dimensions do not match the X11 screen
dimensions.