I have also had some problems with different outcomes when creating a level. For example, I created a level with a box moving through several parts (which were not physically connected). First I made one part where the box came dropping of an edge, next I made a part that catched the box and passed it on, etc. But sometimes when I started making a new part, the outcome of the first parts suddenly changed and I had to adjust it all over again. This happened almost every time I added new things and this was a pretty simple level, think this should be much more annoying when making more advanced levels! Is this a common problem? Would be nice if the outcome of the simulation was completely stable and didn't change from time to time. Otherwise, really great game!