simple, type "sim.frequency=350" into the ` menu (console)
Many scenes change this without notification, for instance, mine.
To fix this, either type it in, or add a box that will touch something upon simulation start. On the "oncollide" script area type in "sim.frequency=350"
The frequency (Hz) is how often the sim checks for collisions.
Movements are calculated frame by frame based upon time (as in 8th grade Algebra)
Springs and stuff put lots of force on them, so the next frame its already past the thing its supposed to hit. For example, the slide (in 100 (default) Hz) flies through the rails its on.
Hope this helps, its pretty simple
EDIT:
I changed the fourth line from "forces ..." to what it is now