Media Catcher doubles usage meter

When using Replay Media Catcher my download meter shows more than double usage in MB. I suspected that something is strange, but I blamed my two teenage sons who share the same account with me.

First I used it for fun, but when I started to download a serious stuff, my 12GB/month limit lasted us only about 10 days. I decided to investigate the problem seriously. I used DU Meter software and results are as follows: Watching 5MB QT movie with Media Catcher turned OFF showed 5 MB usage. With Media Catcher ON the same movie showed 12 MB usage.

Has anybody noticed similar behavior or is it "normal" thing? Or may be all of you who love this program so much are on unlimited usage and don't care?