There's a known issue with these devices and the new Firewire stack that
causes exactly the problem you're describing. I'm pretty sure the
problem turned out to be in the libraw1394 library, and it's since been
fixed, so if you have a very recent version of that library it should
fix the issue.
Otherwise, you can switch back to the old Firewire stack. I'm still
running Ubuntu 10.10 on my music PC so I can do just that on my Saffire
PRO40, which has the same issue; there are some notes on how to switch