In Handbook -> Files and Directories -> Portage files -> User-Specific Configuration: The text should point out that files package.use, package.keywords, etc. can also be directories filled with files containing the configurations. This is a very nice and useful feature that the users should learn already when installing their system, not by luck years later. Reproducible: Always
Hmm, looks like I did this for hb-working-use (bug 196594), but didn't take care of it here. Will do.
Thanks for reporting; fixed in CVS.