I have had that problem many times as well with a My Passport Studio I have (usually when playing video files in VLC or transferring a large number of files). Strangely this does not even occur when it's plugged into USB instead.
Interestingly, my My Book Studio II has not frozen by itself yet via FW connection (but it has when the Passport Studio was daisy-chained).
I usually get around this problem by manually ejecting the drive as well, but I quickly reconnect it afterwards so that Finder doesn't recognize the premature ejection. What I do not recommend, though, is force-quitting Finder, as it almost always results in the dreaded 10810 error and a hard reset.