Shooting on 5D MKIII 1.2.3 firmware, nightly build 29/March/2015.
Settings turned on; mlv_play, mlv_rec, mlv_snd, ettr
CF Card; Lexar 1066x 64gb
Roughly 10 takes had been shot, all of which had been viewed successfully using mlv_play. During 11th take, recording stops midway (I cannot recall the error message) so i assumed the card was full. Upon data wrangling, only 2.6gig of the card had been used. After putting the CF card back into the camera to re-check footage, all but 1 of the takes now had the error message: "File ends prematurely during block header" but it still lists the total amount of images shot within the take.
Magic lantern issue? CF card issue? Card reader issue? I have no idea