Port fails checksum.
(I had failed to warn the author that the FreeBSD ports system,
by default, cares about such things, and he had re-packaged the
tarball about a week subsequent to the initial release. This
changed some dates in comments related to when the documentation
was prepared, but did not actually change the function or
behavior of the software.)
Fix: Circumvention (as reported by others) is "make -DNO_CHECKSUM".
That's fairly gross, though.
Real fix is:
How-To-Repeat: cd /usr/ports/astr/gpsman