There is already a bug report on that same problem (see http://crystalspace3d.org/trac/CS/ticket/320
). It would need to be investigated.
Which physics plugin are you using? ODE or Bullet?
Whatever, a solution would be to use the new implementation of the Bullet plugin which has been improved a lot lately, but you will need to use the trunk version of CS instead of 1.4. It is not sure this will work better but I'm disposed to track down any problems you can have...