So far as I can tell (or at least with the Vincent theme). Here’s a post of mine. The first time, I just linked to the post, the second time I highlighted the entire post, hit ‘reply’ and then grabbed the quote from the reply box (and then cancelled the reply). The first one has only my avatar, the second one begins with Joey_P and doesn’t have an avatar.
This appears to only be an issue when linking to a post in a different thread. When I linked to your post the two different ways, it showed your username (and avatar) both times. I’m also noticing that when you link to a post, you get the link back to the original post, when you quote it, it doesn’t happen.
Where I tend to notice this issue the post is in threads with lots of links/quotes to other threads. Never have any idea who’s being quoted unless you’re told or you click on it to go to the other thread.