This is really a configuration problem. When using the "prefer" tag, you
also tell bbhostgrep to look at only the "preferred" entry in the
bb-hosts file. So you really should have put the network tests on the
preferred entry in bb-hosts.
bbtest-net takes a somewhat more cautious approach, and performs all of
the network tests it sees.
But I agree that it is a trap that is easy to fall into. So perhaps
bbhostgrep should ignore the "prefer" ? At least when looking for
tests to run, which is what it will commonly be used to do. So
I've added an enhancement to bbhostgrep which does that.