Comment 85 for bug 925760

My Comment #84 was a wee bit to quick - sorry. I had wrong (interpreted) timestamps in the kernel log, so I saw log records seemingly from yesterday, but they are from today !
So I had to continue experimenting, and this command (which you could run for every boot) should detach the device, hence power it off and you avoid the flooding of messages:
   udisks --detach /dev/sdb
where sdb is the device causing the messages:
    [Sat Nov 15 23:58:58 2014] sd 5:0:0:0: [sdb] Assuming drive cache: write through
    [Sat Nov 15 23:59:49 2014] sd 5:0:0:0: [sdb] Test WP failed, assume Write Enabled
    [Sat Nov 15 23:59:49 2014] sd 5:0:0:0: [sdb] Asking for cache data failed
If you are unsure of which devices you have 'available' there's several tools available, but these seems to be informative:
   udisks --enumerate-device-files
   udisks --show-info /dev/<your device, like sdb for me>
and also
   lsusb -v