I went to the garage yesterday
We removed the whipers and the cover beneath the frontwindow
What we found underneath wasnt really a surpise
Both the left and right water drain openings were covered with what looked like
a mix between sand, earth and dirt. It covered the openings in total.
No leaves were present, only the dirtmix as i like to call it.
So, we cleaned it out and tested the whole thing by spraying the frontwindow with water.
And guess what..... problem solved.

PS, i never had any problems of this kind with my previous cars (Bmw 320's)
Maybe a little flaw of the xfire design, one which i can live with btw