We just made 4 dugouts, put 2 in a cart after lighting them, one left 2 on the ground after someone said they would bug. When the 2 on the ground cooled off the 2 in the cart were inaccessible, and couldn't be pulled out of the cart, and they also couldn't be pulled out when we initially put them in, just permanently filling space in the cart.
Update: Breaking the cart drops the completed dugouts on the ground, so only the cart is useless when you put the burning dugouts in it.