Comment 3 for bug 654016

Looks like, I found the reason (which still seems a bug in usb-creator).

It appears to create an extra log file .cache/usb-creator.log, looking into which I discovered
too many unmounted loop (possibly mounted by usb-creator):

root@tp:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 474791048 25641620 425031364 6% /
none 1537812 300 1537512 1% /dev
none 1544936 5492 1539444 1% /dev/shm
none 1544936 136 1544800 1% /var/run
none 1544936 0 1544936 0% /var/lock
none 474791048 25641628 425031356 6% /var/lib/ureadahead/debugfs
/dev/loop0 716230 716230 0 100% /tmp/tmpGGyuok
/dev/loop1 708128 708128 0 100% /tmp/tmpa8Piqc
/dev/loop2 708128 708128 0 100% /tmp/tmpGCWILG
/dev/loop3 702610 702610 0 100% /tmp/tmp3lW_H9
/dev/loop4 702610 702610 0 100% /tmp/tmpVTYeFG
/dev/loop5 702610 702610 0 100% /tmp/tmpIGmCbj
/dev/loop6 716230 716230 0 100% /tmp/tmpikHExr
/dev/loop7 702610 702610 0 100% /tmp/tmp9aMXKK
/dev/sdb1 1946972 4 1946968 1% /media/AF1D-90C4
root@tp:~# umount /dev/loop*
root@tp:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 474791048 25641628 425031356 6% /
none 1537812 300 1537512 1% /dev
none 1544936 5492 1539444 1% /dev/shm
none 1544936 136 1544800 1% /var/run
none 1544936 0 1544936 0% /var/lock
none 474791048 25641628 425031356 6% /var/lib/ureadahead/debugfs

Unmounting them, I tried again and, surprise:

/dev/sdb1 1946972 702428 1244544 37% /media/B8AC-EC30
/dev/loop0 702610 702610 0 100% /tmp/tmpX_3XkN

loop0 appeared, and the new segfault again:

Oct 3 18:24:52 tp kernel: [424824.445037] usb-creator-gtk[4252]: segfault at 0 ip 00007fe271595d47 sp 00007fe263debcb8 error 6 in libdbus-1.so.3.5.2[7fe27156f000+40000]