I posted this in another thread, but just so it is here too:
My wife came through on Friday 7th June, she was directed to an e-gate, but instead went to a desk with an officer on after I had told her to get a stamp. The officer looked at the vignette, asked her a few questions about why she was coming to the UK and waved her through. She didn't get a stamp, and was told she didn't need one. Unfortunately she didn't insist on one or ask for confirmation of not needing one, and just accepted the immigration officer's statement.
It really isn't clear what needs to be done in this situation.....