Windfall Tomatoes

I have obviously heard of windfall apples and pears etc.........but never tomatoes before.......why should mine be dropping from the vine some ripe others not? :dh: Any ideas?

 

I don't know John but it is only happening with my small variety not the Moneymakers. It is a few more than one or two. I am wondering whether it is time I harvested them all. I was only picking them as I needed them but there are getting too many ready now. I have already put a lot down in the freezer and given a load to a neighbour. Wonder if they want some more. Won't grow so many next year!