Well, as discussed in
GoFlex Net: Boot from USB while SATA disks connected, both SATA and USB drive may have rootfs under different volume labels, but there is more... While Uboot assigns /dev/sda1 to USB thumb as instructed, kernel in most cases discovers SATA drive earlier than USB and assigns /dev/sda1 to it. Then you have boot problem if rootfs is absent on SATA. To resolve, it was suggested in several threads on doozan's forum by devs to add the thumb's rootfs LABEL to Uboot env, which then handed over to kernel indicating which device to boot from.
Did you try their env var code, and it didn't work? I tried, but may have a different error in env. Reports on doozan's forum say it works when entered as in that thread, but I can't confirm that so far.
You have posted several useful guides, some of them in a form of post in others' threads. They are almost inaccessible now due to many threads with similar titles exist. Consolidate and move them to Guides section, since they were written for users anyway, and don't rich the audience now. There titles can narrow subject matter to certain devices, and Guides section doesn't require content be universally applicable to any current and future device.
You may ask to move select threads back to device section, once obsolete. I would ask
kurlon to consider doing the same. Any guide becomes obsolete over time, it should not prevent it from being most accessible at pick time.