A mailing list peculiarity

[Tron <tron@xxxxxxxxx>]

 I recently signed up for this list  Placed the first post and was very 
pleased to discover how quickly the community responded.  The peculiar 
thing is, every reply I get to my original post arrives in duplicate.  
One copy is to: "users@crater..." and the other to: my email with cc to 
"users@crater...".  Now, is that correct server behavior or am I 
particularly lucky?
:)