GUI Unresponsive when using AMD video card

I installed an old Radeon HD 6750 card and it is causing Gmoccapy to freeze if I interact with the gcode preview window or controls. Clicking any buttons or touching the preview window to pan or zoom locks up the entire Gmoccapy interface indefinitely. The system will continue to mill as if nothing happened and has to be killed with the e-stop. The freeze also occurs in the default Gmoccapy sim, but does not occur in Axis. The system behaves normally when running onboard graphics.

Is there anything I might try to resolve this?

My system is as follows:
Linuxcnc 2.8.2 preempt-rt
The system is running the "radeon" kernel module and driver
Mesa 7i76e
Supermicro x9scl motherboard