A19: I’ve had this, and it is not pick up from the RF cable. What you are getting is crosstalk inside your scart lead. The video OUTPUT From the TV (tuned from an analogue channel) is coupling across onto the input signal from the Humax. When you unplug the RF, the TV has no signal to output, so there is nothing to couple. You can solve this by:
1 - buying a fully screened Scart lead (£10+)
2 - disconnecting the composite video output from the TV at the TV end of the cable (I did it just by breaking the pin 19 out of the connector)
Source: Post2040 by TonyCollinet to Barry’s forum.