There is a confirmed issue with conversion tracking on Google’s Product Listing Ads (PLAs). A Google representative, AdWords’ Bindu, said in a Google AdWords Help thread last night:

PLA’s are product listing ads and if you are using these ads and paying for them on a CPC (cost per click) model, plus you are using Google’s built in conversion tracking, the tracking is not working properly.

Bindu from Google said it has no impact on ad serving, it is only a tracking URL.

Forum discussion at Google AdWords Help.