Anything in Mac OS to interfere with using a disk through a USB hub? Have Modbook Pro with OS 10.10.2 and a powered seven-port USB hub.  A 750-GB bus-powered drive has no problems with the hub in-between.  But a powered drive with three partitions, one of them a Time Machine partition, always gets a failure in backup.  Works fine when the hub is not between.
I have 4 USB 3 drives plugged into my MBP via a powered USB 3 hub and two of them have multiple partitions and different filesystems and all work just fine however the Modbook Pro does not yet support OS X 10.10, so that may be an issue.

From Modbook Support Center:


  YOSEMITE UPDATE
  
  OS X Yosemite Not Currently Supported on the Modbook Pro The newest
  version of the OS X operating system, Yosemite (OS X 10.10), is not
  fully supported on the Modbook Pro.
  
  We do not recommend upgrading your Modbook Pro to Yosemite at this
  time. (Both OS X 10.8 Mountain Lion and 10.9 Mavericks are supported
  on the Modbook Pro.)
  
  An update to the Modbook Pro System Software and the Modbook Pro Pen
  Tablet Software offering compatibility with Yosemite and other
  features will be available in the near future. Check back here
  occasionally for updates.