Emerging pax-utils when linux-headers is not emerged results in an error. Happened to me when updating a 2.4 server system and linux-headers are removed after they have been classified as Blocker for other ebuilds. After (re)emerging linux headers everything went fine.
Uh. Who told you to remove linux-headers? Marking INVALID; good luck compiling glibc e.g. without linux-headers.
Hm, if you read my original Post again, than you know who told me. It's most likely not a bug in pax-utils (thats just the one which raised the issue in my case) but might be a general issue, but resolving as invalid is not a appropriate resolution for this. Other users may tap in here, so think about it.
virtual/os-headers is part of system. If you unmerged it, it's a pure case of PEBKAC, sorry. Unmerging such stuff is _not_ a proper solution for any blockers. INVALID.