Minecart disappears from tracks

My minecarts keep on disapeaing since the version 1.5 upgrade.

I ride the minecart down into the mine, get off, go do some mining and when I come back it is gone. I suspect it only happens if I log out of the game and then come back.

I play on my own local install in Peacfull mode and there is only one rail I use, so it is not other players / mobs taking it or me misplacing it on a siderail.

I dont know if this will help, but it is always parked on a unpowered powered rail. I use the powered rails to break and stop the minecard at the point I want to get off at.