I was spelunking this AWESOME superflat world in which the circumstances are that there is enormous amounts of glass (instead of stone) even though there still is the normal mineshafts and dungeons of sorts. I found a minecart chest and upon looting it's contents, i noticed it was written "container.minecart" instead of "Minercart Chest". I went in and out of it and it still persisted. I hope this strange (but not very world-destroying) bug will be fixed in the next updates.

<3,
-PoeDomo