A209 CLK320 2003 roof not quite closing correctly by rear windscreen

[Stuart Crisp]

My roof closes fine but at the very last moment when the fabric tucks into the rear windscreen, a small section of material about the size of half a golf ball bunches up and sits as a clump on the outside edge of the rear windscreen on the lower right hand corner. If I stop the mechanism from closing the roof completely I can manually tuck the material away and it can then be closed correctly, so there doesn't appear to be any obstruction. Does anyone know how to fix this? Thanks. Stuart