What brand CF cards are you using @jimiz? Are they formatted into exFAT at the very least?
Also were you using '3.5k 1:1 center x5' within crop_rec.mo from ML menu and more importantly did you enabled FPS override to 23.976 while in x5 zoom?
Here's a screenshot from MLVFS webGUI to show that I was able to achieve continuous w 12-bit lossless in both 3072x1308 & 3072x1320 in 24p @ ISO 3200 until pressed stop.

This was used w KomputerBay 128GB 1066x and it was formatted to exFAT via Disk Utility on OS X prior to recording (256GB cards can be formatted in cam while keeping the exFAT).
Settings used under Movie mode within ML:

Thanls for your really important info about!
Cf is a CB 128 GB x1066 tested ,formated exFAT, and seem to work very well with normal raw 14 bit 1920 25p + audio , no stops.
In the setting you talk I become automatic stops , sometime with few beeps and error....BUT I think is some problem her of many another people....
also if you read the setting you do, work on continued recording.... iso and LIGHT of sky example...give a big input data that overwriting buffer and STOP the recording.
With 1920x960 50 P 14, 12 LOSS bit....begine well and suddenly break the recoding, why ? I just do few test before....if I begin recordin in the dark area/room ALL ok....when I turn to the windows light....BREAK recording, so also if was around 60/70 Mb...the light jump over 100.... this do in all the LOSS bit.
i think this is the bottleneck which does not hold recording on some resolution, though not exaggerated and low frames. or not?