Hey Liam, yes it's indeed tracking cart conversions. I must thought about this issue when I coded it as the Piwik visitor attributes are set to „unknown“ in that case. But no tracking would make much more sense. I'm actually not sure why I didn't do this in the first place.. Anyway, this will be changed in the next minor release. Thanks for the heads-up.
Btw, in the meantime you can workaround this by adding the corresponding user to the „Do not track..“ user list before you convert the cart and then removing them afterwards.