nice work @a1ex. I tested new build and now message pops up.
I was/am curious about this error/bug saying cache is locked.
I also can't get 1920x1920 working, can't get any higher than 1728px.
Before the april6 I was able to record square footage.
Not sure if you changed something, or what happend.

Also If I do 3k ISO400 I get a crash when there is to much detail moving.

ML ASSERT:
0
at mlv_lite.c:2036 (compress_task), task compress_task
lv:1 mode:3
Magic Lantern version : crop_rec_4k.2017Apr10.5D3113
Mercurial changeset : 2bbf0bbbaa74 (crop_rec_4k) tip
Built on 2017-04-10 08:54:19 UTC by jenkins@nightly.
Free Memory : 164K + 3162K
hope my data is helping you in any way. if not, just tell me to stop it

cheers!
ps: Is there a chance to get some reference sound back in 3k mode, to have better syncing in post?