On a snapshot multiplayer server I run a few chest minecarts have randomly disappeared from the attached screenshots location. The entities were still marked as there as the detector rail was permanently powered even while removing a 3x3x3 cube around it. Destroying the rail and any blocks around it (leaving void), did not make any physics apply to the invisible cart and replacing the detector rail any time in that spot would instantly be powered. This minecart had been siting in that spot for at least an hour without moving and 24+ hours before then. Restarting the minecraft server corrected the issue.