What does syslog say when you plug the tuner in - if the firmware is valid, you should get a message along the lines of 'found XYZ in a warm state, loading firmware...'. That said, I wouldn't expect it to appear in the webUI if the firmware was bad, but it's worth a check.
lsusb might give you some more info on the tuner itself. lsmod should tell you what drivers it's using, if any.
It's a hybrid analogue/digital device, isn't it? I wonder if that's relevant.
You could try a later version of tvheadend as well, see if that's happier given the change in the way in which the tuner:network relationship is handled - that's easy to install on your laptop, at least (just add the unstable PPA and apt-get update).