Strange video recorder fault?

I have maybe the strangest problem that anyone might have come across.

Our video recorder started playing up, the picture would be perfect for a few seconds, then blared (double image) for several second, then it goes back to perfect, then blared and so on. I did not really think it was video heads that needed cleaning, but I thought I would give it a go. I cleaned them and tested the video recorder on my daughters portable TV using her scart lead, to my surprise the video recorder was working perfectly. I then decided that (a) I had fixed it, or (b) that the scart lead must be at fault.

I put the video recorder back on the main TV, the scart lead gets connected to the Cable TV box. Same old problem. I then changed the scart lead to my daughter one which I knew was working, same old problem. I then connected the video directly to the TV using the second scart socket that the DVD player normally uses (and works perfectly), same old problem. I then disconnected all the scart leads to the TV and connected the recorder to the first scart socket, same old problem. Put everything back to normal and the cable connection and DVD connection work fine. I put the video recorder back on my daughters TV and it still work fine on that. I am now totally confused?