Zigzag edges, corrupted display

Hey Guys!

I've got some problem on displaying objects. This occurs when the Reference (grey beam) display is on, otherwise everything is nice and clear in my own drawing. Both my project and the reference are .dgn.

Working area is around (in meter):
X 414000
Y 93000
Z 0

GeForce GT 630 (latest driver is up)
8Gb of RAM (listen to Daft Punk)

Thanks in advance!