Dell XPS M1530 :: Cursor Jumps Around When Typing?

This has been happening when typing emails in Outlook. It will be interesting to see if it happens while typing this. So far it's been OK. I have a Dell XPS M1530. There it did it just then, the 1530 jumped into the subject field. It always jumps into somewhere I have already typed. So it doesn't just happen in Outlook. It is very annoying. I am using a Bluetooth mouse, but also there is a touchpad just under my hands. Could it be that I bump it by mistake?

I don't know it that's the problem as the touchpad cursor is different to the typing cursor. I'm watching the touchpad cursor and it's not moving. The typing cursor is behaving itself now. I have just moved the touchpad cursor up the screen a bit and the typing cursor is still behaving itself.

While I am typing my hands are well clear of the touchpad. It just jumped again, and it did not jump to where the touchpad cursor was, so it's not related to that.