miniStack disconnects when connected using FireWire port on Thunderbolt display

I am having an issue with a couple of miniStack units I purchased recently. Both units purchased are unmounting randomly during long file copies and I would like to know if you have any advice on how to resolve this issue.

Here are the steps I have taken so far:

• I connected the 1st drive using the firewire cable included and plugged it to my Apple Thunderbolt Display.
• I attached the 2nd drive to the first as a daisy chain.
• I formatted both drives as journaled and encrypted.
• I attempted to transfer 300GB of data to the 1st drive and it failed after approximately 70 GB with a message saying the drive was not properly unmounted.
• I powered down the 2nd drive and removed the firewire cable to remove the daisy chain.
• I attempted to recopy the remaining 300 GB with only the one drive connected and it failed after about 100 GB with the same message.
• I then proceeded to try doing a straight copy to the 2nd drive with the 1st drive unplugged and got the same thing.

I was able to copy over USB, but this is not quite the configuration I was hoping for as it is considerably slower for large file transfers.

Also, I was able to plug one drive directly into my MacBook Pro (mid-2010) using FireWire and that copy worked properly.

It seems to only be when plugging to the Thunderbolt Display using FireWire, which is unfortunately the configuration I was hoping for.

Any advice on what might be causing the unmounting and if it is possible to fix this issue?

Thanks in advance.