"External Source" triggers off of a change in GUI state to QR (quick review), basically this always triggers after picture is taken and the camera enters QR. When "External Source" is off, it triggers off of a CBR (callback routine) that is internal to ML called CBR_INTERVALOMETER. This should be getting called by the ML "core" after each time the intervalometer takes a photo. It appears there is something going wrong here and my cbr isn't getting called (i.e. the module isn't getting notified by the core when the intervalometer takes a photo like it should be). If I have some time and can manage to get QEMU up and running I might be able to debug it, but I have no idea what could be wrong, it doesn't make much sense.