pkg_add -K should preserve the source file's metadata
when saving the destination file in the PKGDIR.
This will make it much easier to compare the PKGDIR
contents with, say, an ftp  mirror... bye eye, or with,
say, rsync. It will also stop needless file transfers
that take place just because some file somewhere has
a newer timestamp, due to perhaps removing files from
PKGDIR and running pkg_add again, mirrors, backups, etc.

Fix: 

Patch the pkg_install toolset to use the fetch(3) functions:
fetchXGetURL()
fetchStatURL()
How-To-Repeat: Use pkg_add -K.