Creatures.tz simulation goes nuts

Running the Creatures.tz example simulation on three different computers (two xubuntu linux, one windows xp) I have seen the simulation start to behave erratically. The "creature" will flail at incredible speeds (even with double gravity in slow speed), usually becoming airborne and bouncing anywhere from 30 to 120 units. After this has happened, whatever progress your breve creature may have made is pretty much lost, as all of the creatures will behave erratically from this point on.