Comment 72 for bug 387161

Here is another JMicron-chip that gives the symtoms listed above and which are fixed by disabling devicekit-disks:

Bus 001 Device 005: ID 152d:2338 JMicron Technology Corp. / JMicron USA Technology Corp. JM20337 Hi-Speed USB to SATA & PATA Combo Bridge

Additionally it seems to fix the similar problem I've had for a long time with my external flash-disk reader:

Bus 001 Device 015: ID 058f:6366 Alcor Micro Corp.

 -- K