I am using Theseus theme as my child theme with some modifications. I tested the original theme too. and I am using the latest wordpress and thematic theme as the parent.
I have threaded comments enabled in the admin section and threaded comments show up in other child themes but not here. related to this; there is no rely link in the comments.
Threaded comments act as expected in other thematic child themes.
any suggestions? unfortunately I put a good deal of work into modification before I discovered this. (comments were the last thing I was looking at styling )