In the episode with the Waldorf salad, as Basil is running into the dining room carrying the Waldorf salad, the audience can be seen "in the kitchen" watching the show !!
Hmmm. At no point in this episode does Basil enter the dining room carrying a Waldorf salad, Sybil does on both occasions. I've been through the sequence carefully, and cannot see what you are talking about. On one or two occasions, Basil can be seen standing at the kitchen table when Sybil goes through the doors, on other occasions, a coat hanging on a coat rack is visible, but I see no other people around.
I did spot one other minor error though. Shortly after assaulting Basil, Sybil sits down to chat to Mr and Mrs Hamilton, taking a cigarette out of the packet as she does so. In the next shot, the cigarette is already lit and smoking.
I watched this episode carefully, and although there were many mistakes, the only thing thats strange about the kitchen is that there is a coat rack, and a lady who is obviously on the production team. One thing that is strange though, is that the fridge disappears. Sometimes you can see it through the door, and other times it is gone.