Issues:
13w02b server generates faulty landscapes. When you go to the area affected you get stuck in a block because the game registers the place of the block but the view does not render it visual causing the user to become stuck in the same area.

steps to recreate.
1) generate a new world.
2) look around till you see faulty area.
3) Walk into faulty area.

Screen shots
http://s8.postimage.org/yrbboo1et/Screenshot_from_2013_01_13_14_52_57.png
http://s2.postimage.org/ujsnq4ya1/Screenshot_from_2013_01_13_15_14_27.png

FYI> having issues with your attachment system.