Thank you for the info tnicoson, it was very helpful. The issue seemed to resolve itself, although at first it did sound like there was a very slight pitch bend in the tone for a few seconds before it completely righted itself. If I have the same issue again, I'll know where to look first! Thank you.
I wasn't sure what title to give this weird problem. I've had the keyboard several years with no problems up to now. Singing along to something I was playing today it seemed higher pitched than usual and on checking, although I was playing in the key of D it was actually the key of E (hope that makes sense!). The keyboard isn't showing as being transposed. The weird thing is the accomp still plays in the right key (so I can't play with accomp). I've tried everything I can think of to solve the problem including returning the keyboard to factory settings. Is there something I'm missing? OK after spending hours trying to solve this problem it now seems to have solved itself :-)