A WebmasterWorld thread reports that several webmasters have noticed that even though they are redirecting their non www to the www version, Yahoo is still listing their non-www as the main result.

This comes even after months of redirecting the non www using a 301 redirect, permanent redirect, to the www version. Here are some comments from the thread:

Is it a backlink issue? Doesn’t appear so:

So what is going on with the latest Yahoo update? Good question.

Forum discussion at WebmasterWorld.