OK, this is interesting. One other user with this problem is running 3.1.1, so it's not limited to 3.0.*. I do not know if they are running PyeTV. I am not sure why the PyeTV component would be a problem with Poke Eye. Both (presumably this is true for PyeTV) just send AppleScript commands to EyeTV. However, if PyeTV is the key here, that would be very interesting.
For what it's worth, there is some special handling in Poke Eye for EyeTV 3.1.1. There's a bug in it which means the command which should go into fullscreen simply isn't there. However, there's another that does it :-)
I assumed that that command problem is only in 3.1.1, but this is easy to test with a couple of scripts I have, if you don't mind opening the Terminal application.