I would hazard a guess that its a dodgy wiper if it didnt do the same with the old one ? Have you put an aero wiper on the rear because some makes of aero wipers are unsuitable for the rear ?
 
It just sounds like your wiper isnt flexing enough.

Ive got the polo aero rear wiper on both of mine. They work and look much much better than the standard ones.

You need the arm, cap and blade, which is about £20 from VW.

Although if you do go for this, then get a wiper blade for a 2007 onwards passat estate, that wiper is shorter than the polos so it fits on the screen! (Lupos are fine with the polo blade though).