Moira Brooker (Judith) admits to occasionally being so mesmerized by Dame Judi Dench's talents while taping, that she would forget to say her lines.
Between Season 4 Episode 10 and Season 5 Episode 1, the layout of the interior of the house changes. Formerly, standing inside the living room, there was a wall outside the living room door, which the door opened from the right. Now, the door opens from the left, the wall is gone and you are able to see the front door of the house from the living room. In Season 9, the door opens from the right again.