I use facial expressions when genuine... I will have a sad face if I feel sad with them, happy if there is good news, etc.

Sometimes T's use facial expressions as a way to make the client aware of how they are presenting themselves. I had a client who had very incongruent affect. She would be talking about something sad, but her affect would be smiling and vice versa. Sometimes T's would use this as a way to clearly demonstrate to how they are responding to the clients story...

If it's something that's uncomfortable at all, I'd mention it and talk about it.