dangling trees

In todays 2.6 git repo, I see the following:

$ fsck-cache
expect dangling commits - potential heads - due to lack of head information
dangling commit 897f5ab2cd733a77a2279268262919caa8154b9d
dangling tree c39ae07f393806ccf406ef966e9a15afc43cc36a

The dangling commit is the current head - that's fine.  However,
what's this dangling tree?

It appears to have come in from Linus' tree on kernel.org this morning.

(above from cogito 0.8)

-- 
Russell King