This happens when a pony is stored for many years, the plastic get squished out of shape.
Leave a Whisper has suggested the best method for fixing them
very hot water (just boiled), dip the pony part that's affected in and allow to cool. Sometimes you do need to use a leg brace (something like a pen) to hold the legs in place. It may take a couple of treatments to fix so don't worry if it doesn't work first time.
The heat works by reawakening the plastic's memory
Love pkw xxx