Google Webmaster Tools is a nice, FREE service that can give webmasters clues about what needs to be fixed on their websites. Like all free services I am aware of, it is not perfect.
For Example: The “Duplicate Title Tags” section in Webmaster Tools for this website always shows duplicate title tags for the most recently published items. The duplication exists between the RSS feed and HTML versions of the same page, even though canonical tags are implemented.
Why? I’m guessing that the part of the algorithm that consolidates the items with like canonical tags comes after the detection of the duplicate title tags.
There is always a significant delay when using Google Webmaster Tools. Sometimes it takes weeks for updates to be reflected. So don’t panic! If you know it’s right on your end, most likely it will eventually be reflected in Webmaster Tools, and in Google’s index and results.