Hi Peter,
Still waiting on verification, however I think you're right about the bitslip. Have you tried inverting the frame clock? This is the only way I can see that you would get 4,0,12,8.
Note that the default case is 12,8,4,0, not 0,4,8,12 as you mentioned in the first post. With a bitslip of 2, the pattern would be 4,0,12,8.
Regards,
Matt Guibord