Why is possible to go through minecart?

Watch the video
http://www.youtube.com/watch?v=ye51JGa2aW8

As shown on the video, in 1.4.2 i can go through a minecart. This is a sad bug.

Comparing to 1.2.5, i just can push a minecart (and can't go through her)

Mojang, fix this!