1. Put down two minecarts near eachother on two different rails.
2. Get in one minecart.
3. Right-clicking on the top of the other minecart will enter it, but clicking near the rail/the bottom of the cart causes your window to jump.
Note: This "jump" will also occur if you right click the minecart you are sitting in.
MC-14524 Right Clicking On Minecart / Pig / Boat While Riding In It Tries To Remove You