Wrong graphic memory size #GPU

Hi, when I boot on Mountain Lion using chameleon with GraphicsEnabler=Yes, I get the name of the graphic card in System profile, but without the VRAM property.

During the chameleon log, when it detect the graphic card, It show 4096MB of memory instead 1GB. =/

Note: The kext, ATI5000, GraphicsAccelerator and AMDSupport are loaded.

How to get the correct graphic memory size?