Platform: FreeBSD 8.0-RELEASE i386
hpt/fbsd 1.4.0-sta 16-02-06 from ports (husky-hpt-devel-1.4.r5)
When packing netmail from a JAM area, hpt inserts junk into outbound packets around the INTL, TPT and FMPT kludges. This does not happen if netmail is kept in a MSG area.
How to reproduce: configure hpt to store netmail in a Jam area, toss and pack a netmail message, view the resulting packet with catpkt or any other viewer.
Workaround: don't store netmail in a JAM area.