I have the same problem, but only with two Western Digital USB 3 drives. The drives are My Book Essential 3 TB (WDBACW0030HBK) and My Passport Essential 500 GB (WDBACY5000ABK). I can reproduce the behavior on a laptop and a desktop, both running Ubuntu 10.10. All other drives remain unmounted.
I have the same problem, but only with two Western Digital USB 3 drives. The drives are My Book Essential 3 TB (WDBACW0030HBK) and My Passport Essential 500 GB (WDBACY5000ABK). I can reproduce the behavior on a laptop and a desktop, both running Ubuntu 10.10. All other drives remain unmounted.