bootp server port open

A security audit of a network I designed found
that port 67udp is open on two “sets” of
routers/switches. The routers are part of
redundancy groups, so there is a primary router
and switch with an etherchannel connection to
the secondary switch and router. Although “no ip
bootp server” is configured on the routers, the
port is open on all four devices.
This is true for two locations, with the exact
same config/topology working just fine on about
25 other locations.
Since this port is open along the “link” between
the two routers, it seems like some sort of
session is open, but the only communication
between the two routers is HSRP and IBGP.
Any ideas why this could be?