Hi there, to make some progress I propose
to keep this issues about sending Precedence:bulk.

a) point to some documents that describe precedence header intended and real behaviour
b) try to find the point (commit) where this was introduced and the reason for it.
c) Check out some examples. The nosy detector for issues.roundup-tracker.org itself
is send to the mailinglist and it seems to work (I don't know precisely why).

I agree that mail loop prevention is important, I have also seen email loop clutter up a full 
company internet connection within a short timeframe.