The vim gentoo-syntax highlight doesn't works in files like /etc/portage/packages.[use,keywords,mask,unmask,...]/*. It works well in /etc/portage/packages.* file. Reproducible: Always
Fix is in svn, a new version will be out shortly.
Version 20080717 is in CVS which fixes this. Thanks for reporting :-]
I believe this fix broke syntax highlight for "vim /etc/portage/package.use", it only works without the full path.
Created attachment 161364 [details, diff] Proposed fix
I just changed from the package.* files to the directories and patched gentoo-syntax-2007-05-06 for myself. I wanted to submit the patch when I found this one, so I decided to upgrade and I don't encounter your breakage. The portage patched version works just fine. (20080717-r1)