[Note: I removed the links and username, since it's an flocked entry.]
The comment by a user is not visible while reading the post, though it is not screened, the entry is flocked, and she has access as a member of my flist. THe only way it can be seen and replied to is using the reply-to from inbox and Reply from the mailed comment in my inbox.
If it is replied to, however, the comments become top level comments and the user's reply reply is still invisible.
Clicking on a direct link to comment goes to the entry and does not show the comment.
*scratches head* This is just--bizarre.