acceleration

I have fabia scout diesel estate when I drive along and slow down, say in 5th gear and don't change down a gear soon enough the engine takes over and I can drive with no feet on any peddle,like driving automatic the cruise control is off,it happens in any gear but if I need to slow down in traffic,say from 3rd to second and do not do it quick enough the engine accelerate,i have had to skoda garage and told this is the revs compensating for some reason and is natural on all diesels,i have had the car a few months now and never notice it before and has seemed to get worse,my wife will not drive the car,as she says the car could rev up in traffic and run into the back of other cars,is this normal??????????