[pfuetze]

what you you can do is bending the rails with a small screw driver at the place where the nose of the rail goes into the U-shape part. just a little to help it making better contact. 

and always be sure to have the braids on your cars adjusted right (a little feathered out, bend downwards)

this problem is not common and what i can imagine can only happen when the track is not flat on an even surface, but you ´re trying to make some uphill - downhill sections. 

anyway i hope that this helps, was my description clear enough for you?

Peter