Control: found 3.3.2-5+deb8u1 It's probably the patch which was released a few months ago in testing and a few days ago also in stable as 3.3.2-5+deb8u1 is also affected. As can be seen here: http://unix.stackexchange.com/questions/258790/
Try reversing the patch locally and see if it fixes your problem: --- a/lib/udev/rules.d/64-md-raid-assembly.rules +++ b/lib/udev/rules.d/64-md-raid-assembly.rules @@ -25,6 +25,9 @@ GOTO="md_inc_end" LABEL="md_inc" +# Disable incremental assembly to fix Debian bug #784070 +GOTO="md_inc_end" + # remember you can limit what gets auto/incrementally assembled by # mdadm.conf(5)'s 'AUTO' and selectively whitelist using 'ARRAY' ACTION=="add|change", IMPORT{program}="BINDIR/mdadm --incremental --export $tempnode --offroot ${DEVLINKS}"