When you send a minecart off somewhere and it hits an un-rendered area it stops and wont go until you go find it. I'm not sure whether this is a bug or it has been always this way but if it is a bug then here you go.
Comments 3
This behaviour is intended? Truly? Why?
I noticed this very recently after launching an empty (stock generic) minecart down 1200 m of powered rails. Once the cart had disappeared from view, it stopped moving - unless I went after it. But, when my character rode in the cart, it completed the trip normally (as might reasonably be expected of a real minecart), bounced off the end-block and returned to its launch point, as expected.
As a follow-up experiment I placed Detector Rails at 100 m intervals over the full length of the tracks, ran Redstone alongside them back to the launch point and then terminated the circuit with a Redstone Lamp just for lulz. The lamp winked three times, not the twelve it would have had the minecart not had this surprising and inexplicable behaviour.
I do wish you would fix this. This behaviour may be intended, as you said but, quite honestly, it is indistinguishable from a real bug.
This is intended basic Minecraft mechanic.