When in Adventure Mode, if you attempt to pick up your minecart after you have journeyed on it it disappears! This bug has been going on for nearly a year, and you new version has not fixed it, so I joined the bug tracker team today. It is playing havoc with the adventure games I am building.

So to confirm, whether a minecart is resting on tracks or on the ground, when you hit it to pick it up it disappears.