Brian Turner is reporting at a Platinax Forum that Yahoo has changed the way they handle 301 redirects.
In the past, according to Yahoo! Redirect Handling Rules (PDF File), a 301 from Site A to Site B, Yahoo would keep the target URL. If the domain remained the same, it would not necessarily be the case, see the PDF file above to see the detailed rules.
Brian is claiming that Yahoo is now looking at the authority of the domain and if the domain has more "authority" than where it is 301 redirecting to, then it would keep the source (the more authoritative domain) as the main URL for that site, regardless of the 301.
Honestly, it seems like Brian tested this out on one domain. To me, this seems like a glitch on one particular site. We have no other reports of this in any of the other forums or any confirmations from other SEOs or webmasters on this topic, at this point in time.
Forum discussion at Platinax Forum.