I found a glitch in auction system, when leaving feedback. You can leave double feedback for same thing if you do it like this (I just noticed it so better to report it right away):
My control panel -> Selling -> Leave feedback
Now you check the auction which you want to leave feedback, write a message & post it, & it showed 2 feedbacks.
Cheers!
Merry Christmas!
Glitch in auction feedback
MetalHawk