strange list behavior when replying to message on list

Hi all, I'm wondering if anyone else happens to be using Mozilla Thunderbird and seeing this behavior, and also if this behavior is a feature or a bug. When I hit the reply button to respond to a message most of the time the actual sender's address is the one the message is being sent to rather than the list itself. This is the first mailing list I've been on that I've seen this behavior; all other lists I'm on when one hits the reply button, or CTRL+R the mailing list's address is inserted as it should be and is expected. I know with some email clients there is a menu item specifically there for responding "to the list" based on whether or not there is a list-header in the header information but that isn't an available option with Thunderbird. Is anyone else seeing this behavior or is there something I'm missing? Mark