This is a huge bug, but I have not tested this in 1.4 yet. The issue is that there are directional issues with minecarts, redstone, etc. that include directional block placement. For example, when making a minecart station of sorts, sometimes, the rails do not position in logical order, bugging out the minecart on the track.
I believe that the bug is caused because the blocks are programmed to a specific direction, and bugs out when it isn't facing that specific direction.