Whilst in gravity, player can not enter a space 1.75 blocks tall, yet while just aligned to the ship and not in gravity, you can.
1.75 blocks being a full block and the space left by a 1/4 slab, like so http://puu.sh/lC3Ul/bf007c7755.jpg
Building a hallway as described and moving through it in gravity or with out (alignment doenst matter as long as it would visually fit) s causing that problem.
increasing priority because this severely limits building designs