The latest 2.6.8.1 kernel puts the '.1' in EXTRAVERSION, which the kernel-2.eclass obliterates - thereby making the built kernel appear to be '2.6.8', not '2.6.8.1'. Throwing a K_NOSETEXTRAVERSION="1" in the ebuild ought to fix it, but I'm not sure if there is a better approach.
Using K_NOSETEXTRAVERSION is OK. Thanks for the hint, it's now fixed in CVS.