When you put multiple carts together on a track and push them together, they explode without any power tracks.
http://www.youtube.com/watch?v=90Q0uUwS2fs
Environment
Macbook OSX 10.8.2 2.4 GHz Intel Core 2 Duo 4GB 1067 MHz DDR3 Late 2010
Minecraft Launcher
Duplicate of MC-7867, please use the search function to see if your bug has already been submitted. Currently over 53% of tickets are being closed as duplicate.