Comment # 8 on bug 70409 from Vitaliy Filippov

(In reply to comment #7)
> In Vitaliy's case, the problem is the lack of glamor support in Debian sid.
> This is fixed in the X packages in Debian experimental.

Ah, ok... but it seems experimental has no actual xserver-xorg-video-radeon
package... so I should probably rebuild it by hand :-(