Wipers sticking help?

My wipers keep sticking on the windscreen which restricts my view when there on speed 1 and not returning to park mode and after about 20 seconds I flick the switch bk to park and speed 1 again , the wipers move and stick again. I have to keep doing this several times before they get back to its normal state :/ any body know any ideas? Speed 2 and 3 are normal it's just when I put the wipers too off/ park mode it sticks