Also, in this case, the same distfile is also used by other
  packages. It shouldn't be retrieved to a DIST_SUBDIR. The reason, it
  worked for others (like bulk builders) is that they had previously
  downloaded the file (maybe for a previous thttpd or for another
  package).

I commited the change to thttpd's Makefile to reference it from
DIST_SUBDIR, which seems the minimal fix given the freeze.

I have no objection to un-DIST_SUBDIR-ing all of thttpd or just this
file (although I don't know how to have a pkg with DIST_SUBDIR for
some distfiles and not others).

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