I was thinking that recent pax (from NetBSD) had this problem fixed. (I
  will have to look again ...)

Not sure what 'this problem' is, but quagga made a distfile that mixed
tar format flavors (create by automake, and then append by hand).  Of
course this was broken, but pax couldn't read it.

-- 
        Greg Troxel <gdt@ir.bbn.com>