1) the detection of a successful mount is done by the command exit code; if it's zero then is successful, if not, it show as an error. Maybe mount is trowing a non-zero exit code when the dirty flag is set even if the mount routine itself is successful.
2) the diskinfo.log file is the file you want, but I saw no PHP errors there that could lead to a daemon stop. Maybe the system is killing the daemon in a, out-of-memory event.