We've got a Toshiba widescreen rear-projection TV, and an 'el cheapo'
DVD player. The problem is that when playing DVD's which are in the
4:3 format, the TV keeps switching between 4:3 and widescreen, after
the DVD has been playing for a few minutes. It seems to work OK with
widescreen discs.

So, what do people think, is there a fault with the TV, or the DVD
player?

The TV switches OK with our el cheapo Freeview decoder, putting in
grey 'curtains' when showing 4:3.