Could you add card model? I just tested on my test machine, and it surely accepted:
Virtual 4096 4096
Can you add the output of 'xrandr'? Here's mine (HD5850, 09:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Cypress LE [Radeon HD 5800 Series])
Screen 0: minimum 320 x 200, current 2048 x 1152, maximum 4096 x 4096 DFP1 disconnected (normal left inverted right x axis y axis) DFP2 disconnected (normal left inverted right x axis y axis) DFP3 disconnected (normal left inverted right x axis y axis) DFP4 connected 2048x1152+0+0 (normal left inverted right x axis y axis) 510mm x 287mm 2048x1152 59.9*+ 1920x1080 59.9 1680x1050 60.0 1400x1050 60.0 1600x900 60.0 1360x1024 60.0 1280x1024 60.0 1440x900 59.9 1280x960 60.0 1280x800 59.8 1280x768 59.8 1280x720 59.8 1024x768 60.0 800x600 60.3 56.2 640x480 59.9 CRT1 disconnected (normal left inverted right x axis y axis) CRT2 disconnected (normal left inverted right x axis y axis)
See comment.