Sorry for bad English, I speak french.

I find a bug whit minecarts that allows you to travel whit no rails. So the way I discovered it is that I made a circular track, with 4 powered rails and 4 normal rails. I put 4 minecarts in the same block by clicking on the rail. After that, I push the minecarts and it starts mooving. I beak one powered rail and here it goes. The minecarts get out of the track and starts to travel whit no rails. It only stop when there is a collision or less that 3 minecarts.

Also, I found an other bug by doing this.

When you have done your circular track and push the minecarts (put more), Put another minecart while the other are moving. The minecarts are gonna stop in a corner and continue to "move" (there is the sound) but there are not really moving. There are like bugged in the corner. And then, when you break the rail under, it makes the first bug.