Render Engine not good

Sorry my english, i'm speak german.

Play with the new server version 14w25b

i have build a long tunnel over 2000 blocks and installing minecart. if i driving with the minecart, the render engine dont work. after short distance, i'm driving in a black world. if i stopping the minecart and walking, the render engine don't calculate the map. i stay in a black map without orientation. i must stopping the game and joining again. but after short distance i stay again in the black world.
the snapshot its not playing.