Apoligies if this is explained in the user manual but I can't locate it at the moment.

Whilst browsing the program guide I noticed that E4 had a yellow square just before the time. Now I know that a red square means there is a tuner being used to record that channel and the green square means that there is a tuner being used to view that channel but I don't think I've ever had a yellow square. I Don't know what I did to get this yellow square, and it appeared that whilst channel hopping and checking the technical setup menu in-between that both tuners were being used (i.e. one tuner wasn't tied to E4). An oddity though was that when I tuned to E4 the play light lit and the blue circles came on as if I was watching a recording although E4 was showing as normal. Channel hopping away from E4 would cause the play light and the blue circles to go out. Returning back to E4 they would return. Pressing the stop button whilst on E4 cleared the play light and the blue circles and E4 remained on-screen as normal. Following this the program guide no longer showed a yellow square next to E4. The box appeared to be OK but I gave it a quick power cycle just to be on the safe side.

Anyone any ideas?

It just means you're buffering the channel. I guess you pressed pause and switched tuners, it'll keep time-lagging that tuner until you return to it and press [LIVE].

Just tried what you said - never knew you could buffer the channel like that.

Anyway I noted that the program guide put a light yellow square to signify the channel was being buffered and that it tied one of the tuners up (as expected). However what I saw earlier was that it was a darker yellow square and the tuner wasn't tied to the channel it would have been bufferring. In fact the guide showed two green squares next to the channels that I had channel hopped to/from as well as the dark yellow square on E4.

Not seen that before though as you probably know there's no reason why it can't de-mux more than two channels acros two muxes (if you record stuff off two separate muxes and go into the engineering section you'll see the first two channels from those muxes displayed, you can get two recording and two playing back this way).