Yahoo is somehow discovering and indexing dynamic version

[Asia_Expat]

A few weeks ago, I switched my forum over to re-written friendly urls. It's not a hack, because the new IPB 3 software that I use comes with FURLs out of the box.

I've configured to 301 old dynamic versions to the new FURLs and TESTED THOROUGHLY, even using the header checker here at Webmasterworld. Everything is set up correctly.

Google has already started recognising the new FURLs and indexing them over the old version, so I'm totally convinced all is technically correct...

However...

I just noticed a thread that was started a few days ago (i.e. there was never any dynamic version of the thread available) in the Yahoo results listed in it's dynamic version!
Immediately, I checked the server headers for that thread... 301 from dynamic to FURL... all is technically correct...

How on earth is Yahoo finding this version and indexing it?!

[Asia_Expat]

It's just dawned on me... the forum RSS feeds that are displayed on my static html pages are still showing the dynamic version (but they're 301'd to the FURL) and are not scheduled to be updated to the FURL version until next week. I thought it wouldn't cause any issues in the meantime.

So, Yahoo can't handle 301's, reads the anchor text and indexes that instead... pffft.