I've discovered what I think is the underlying reason for many folks reporting similar problems. I bet that I can predict the GUIDs of the drives/docks/cases you're having trouble with! I bet that if you look in Disk Utility, if you click on the drives, you'll find "Connection ID 13757101839304263"!
Oh and if you look in System Profiler and click on 'FireWire' or 'USB' you'll find the GUID 0x30E002E0454647 !
What are the odds? I shouldn't be able to predict them; theyr'e supposed to be unique, after all, but google that number and you'll see that a great many devices all use that GUID. (13757101839304263 in decimal is the same thing as 30E002E0454647 in hex.)
Mac OS seems to rely on them to be unique, and has fits when they aren't. I haven't found a total solution yet, but in the meantime, running this in Terminal can help:
sudo kextload /System/Library/Extensions/IOFireWireFamily.kext/Contents/PlugIns/AppleFWOHCI.k ext/
Sometimes it helps to run this first to unload before loading the kext (kernel extension):
sudo kextunload /System/Library/Extensions/IOFireWireFamily.kext/Contents/PlugIns/AppleFWOHCI.k ext/
Enter your password if/when prompted, of course.
In most cases, if you contact your hard drive manufacturer, they'll provide a utility that will fix the drive so that it actually has a truly unique GUID.
I'm mad at Cavalry for hiding the problem and refusing to fix it, W.R.T. the two 1TB HDs I bought from them for around $500, when that was the going price.
I figured it'd be helpful to create a user tip off the discussion in this thread: Disk Drive ejecting itself - https://discussions.apple.com/thread/2151621?start=615&tstart=0 This is my first attempt to create a tip. I'm not sure I'm doing it right, but here goes.