Messages Duplicated to Similar List Names

[Istvans]

We have 2 mailings lists for students: One is called
"undergrads", and the other is called "grads".

When a message is posted to either list alone the
messages process correctly. Subscribers receive only
one copy for each list to which they are subscribed.

However if BOTH lists are included in a single TO: in a
message (So To: grads@host, undergrads@host)

the end result is 3 (THREE) messages:

One message from [Grads]
One message from [Undergrads]
One message from [Grads][Undergrads]

these lists are not configured to be umbrella lists.

All other lists behave correctly so if messages are
sent to the lists called: Faculty, Staff, General the
message processing behaves correctly. A single message
addressed as follows:
TO: staff@host, faculty@host, general@ host, grads@host
delivers only a single message to each subscriber.
However if the To is modified to include both the Grads
and Undergrads a message will be sent to
[Grads][Undergrads]

The only issue seems to be with the word "grads" being
a complete subset of the word "undergrads"

[http://sourceforge.net/tracker/index.php?func=detail&aid=1104646&group_id=103&atid=100103]

[Tokio Kikuchi (tkikuchi)]

This does not occur in my similar environment. Isn't this a
MTA problem? It might occur if you are using procmail as a
local mailer and utilizing regular expressions in sorting
the messages.