Right, the first thing to do is make 100% sure its a bug, and not a configuration error or something like that. If you need help with your config then e-mail me at email@example.com.
Next thing is to check if the problem has been addressed in the FAQ.
If you are sure its a bug and it hasnt been addressed before, then please e-mail me at firstname.lastname@example.org with *ALL* the information you can give me. This includes the output that Q3Log produced, the circumstances in which it was run, your config file, the command you used to run Q3Log and any other information you think would be handy to me.