Minecart with hopper dissapears when chunk is unloaded.

I built a tree farm that uses a mine cart with a hopper to collect tree saplings after I harvest the trees. The problem occurs when I leave the area and the chunks unload. When I return about 50% of the time the mine cart goes missing. It doesn't matter if the mine cart with a hopper is loaded with items or not. However I have noticed that it only occurs when the mine cart is in motion when the chunk unloads.