It turns out there was a bug in the yt autoupdater, which I believe I have now fixed. You can manually update your yt installation by changing to the yt source directory (which "yt instinfo" will provide correctly) and typing:
hg pull hg up python2.6 setup.py develop
And now, once again, "yt instinfo -u" will update you to the current tip of whatever branch you are on.
Sorry about the bug.