pncook:Thorny, I have been fiddling with my screen for the last day or so to fix an issue with a BD player (which I have now done). I have a Pioneer PDP-436XDE which is about three years old, it's the one with the separate media unit and it too has two HDMIs (Inputs 3 and 4). Like aliEnRIK my screen has Input 4 permanently set to HDMI but Input 3 needs turning on in the menu screen. Once on nothing else is needed as my screen copes with what is sent to it. My Sky+HD is on an older version HDMI cable (QED HDMI-P which isn't v1.3 but I think 1.1) and connected to Input 4 as 1080i, everything fine (in fact upscaled by the Pioneer to 1125i automatically). Prior to my Pana BD50 I had a PS3 connected to Input 3 and set to output 1080p which again was handled correctly by the Pioneer, even upscaling it to 1125p which is what it does with my BD50 and Chord Silver Plus 1.3 HDMI cable. I thought that HDCP was first supported by Pioneer's 6th Series of Plasma and not before (e.g PDP-436...) but there's an excellent Pioneer support site which you should register on and I'm sure that was one of the FAQs I was reading. At any rate they have helped with my aforementioned BD problem which is on another forum thread here at What HiFi? Good luck in getting sorted.
pncook - thank you so much for your reply, I have actually just got off the phone with Pioneer who were genuinely very helpful - makes a lovely change from most 'customer service' people. My plasma is actually the previous gen to yours with one hdmi on input 3 which i have turned on.
The pioneer guy basically said this is a known issue with my tv and that the problem comes from the sky box and their content protection (HDCP) - this also then affects anything plugged into the HDMI port.
As a temp fix I can plug stuff in through component but he said to fill out the form on the website and someone will be in touch to arrange an engineer to come out with a new circuit board which would cure the problem - perfect!