I have run into the exact same problem as described in the original posting. But unlike RhialtoFalu, I cannot seem to resolve it.
Flushing the log doesn't seem to work for me. Neither running "logcat" nor the "pastlog" command work: Instead, both commands hang hard and and cannot be killed; I have to close the terminal after running them. :-(
Maybe it's possible to clear out the log manually... Any idea where it is kept? The debug messages appear in a source code file linux-18.104.22.168/drivers/staging/pastlog/mmc_past.c, so it's perhaps a static flash partition?