My k750i has the same problem. But I havn't flashed, I just upgrade the camdriver0.dat.
Have you backup the camdriver0.dat? I compare the drivers and find out that
cam_ss_sync=7 (version 3.8) change to cam_ss_sync=f (version 6.0).
And I edit the new driver, it work.
May be the old machine can't support the new setting. My k750i's firmware is the first version.