If setting MLV_SND to 8kHz the camera cannot record (or save recording). The recording seems to go fine, but when stopping the menu gets inaccessible and you have to reboot camera. To replicate the error: set MLV_SND to (8kHz, 11kHz or 22kHz) and record. Try stop the recording. Notice no camera-led blink (as when normal). Menu gets inaccessible and you need to pull battery (just tried restart fucked up some buttons in camera menu?). On card you will now find the MLV-file with 8 (always?) Mxx files only 52Kb large.
To avoid just set MLV_SND to 48kHz or 44.1kHz
Build May5th e5939c727eb4