Some Minecart physics are broken BUT only on servers.

(Next statements are referring to the close-up)
Procedure: Placing the Minecart right infront of the wooden block and entering it right away.
If you drive down the left path, you will end up 3 blocks behind the slime block (as shown).
If you drive down the right path, you will end up on the edge of the slime block (as shown).

If you put another entity (tried it with donkey) into the Minecart then this behavior is reversed.

In single player you always end up 3 blocks behind the slime block.

I've tried some configurations (wide picture) - the ones with red concrete are effected by the bug, the green ones work as expected.