DisplayLink kills X on Xorg > 1.19

[zachzundel]

When I use xorg-server version 1.20 or greater, trying to send output to the monitors through xrandr kills my X session and boots me back to a login screen. Switching back to 1.19 does the same. I can't see any obvious issues in unencrypted logs, so I'm posting this hoping that the problem can at least be isolated. I'm happy to submit a patch to evdi or X if that's what's necessary.