[Nafi]

@Milhouse 

it seems the issue was caused by my xorg.conf. In the early days, i added some modelines because some resolutions/refreshrates were not detected when HTPC was connected to my AVR.

without that custom xorg.conf, the issue seems to be gone. It seems to be useless anyway since all the needed resolutions are available without it.

thanks for guiding me into the right direction. BTW, I also tried that enable_fbc kernel parameter (with 0 and 1). It did not make any difference.