I can confirm the exact same behavior as described above, but on my iMac. I'm using the 0.8 version of DeSemuMe and my hardware looks like this:

  Model Name:    iMac
  Model Identifier:    iMac7,1
  Processor Name:    Intel Core 2 Duo
  Processor Speed:    2.4 GHz
  Number Of Processors:    1
  Total Number Of Cores:    2
  Memory:    4 GB
  Bus Speed:    800 MHz
Video
  Chipset Model:    ATI,RadeonHD2600
  Type:    Display
  Bus:    PCIe
  PCIe Lane Width:    x16
  VRAM (Total):    256 MB