Steps to reproduce:

1. create a slope with rails that goes into a single solid block that has air above it
2. let a minecart go down the slope
3. watch the minecart glitching into the block or even going through the whole block

if there is no block below the block the minecart is driving into, the minecart also can fall through the block potentially killing the player/mob because they might suffocate. The images show the result of the bug.