Send= owners
           ^
And are you the 2nd owner?  I believe that Owners is not a standard option
                                                ^
for Send= but rather only Owner (singular) and other access levels.
 
The arrangement you want is Send= Editor and then set two Editors.  In
this arrangement, submissions to the list will go to the first editor
only, but either editor can post.  In your current arrangement, postings to
the list address from anyone other than the first owner should disappear.
 
-- Roger Burns   [log in to unmask]