OT: Why does this list spam me with subscriptions to other lists?

["David A. Desrosiers" <desrod@gnu-designs.com>]

Every time I compose, send and confirm a post to this list, I am 
spammed with almost immediate requests to subscribe to 3 completely 
unrelated Yahoo! lists at this address. EVERY... TIME!

They are as follows:

(2676) Please confirm your request to join lightenlife
(2498) Please confirm your request to join Team4PortlandParks
(2683) Please confirm your request to join FictionFactor

These request come directly from posts sent to this list.

Is there some subscriber bot on this list who is harvesting everyone's 
email for the purposes of spamming the members of the list? If so, 
their subscription to this list should be blocked/terminated. It's 
getting quite annoying.

Is anyone else getting these for every post to this list as well?