Alex: Works fine for me. Can you extract the files in question using the commandline tools? Does it open a BetterZipQL window or a plain QL window for unknown types? The former should at least have the table heading and everything above that.

You can run this command in the terminal to get some diagnostic output (replace the last bit with the absolute path to your file):

qlmanage -p /Users/robert/Desktop/testfile.tar.bz2

What does it say in the last few lines?