I discovered a quirk last night.
When I tuned to Film 4 I got an on-screen message saying Film 4+1 would be moving and I needed to do a retune; Press OK to dismiss this message. I did so.
I then wanted to see the Information banner for the programme so again pressed OK. Nothing happened. I changed station and OK brought up the banner. I went back to Film 4 and OK still did not bring up the banner.
It therefore appears that after you have pressed OK to dismiss a retune message, OK does not work on that channel. It obviously starts working again at some stage but I haven't tracked it down when.