Yes! Me again, with the same bug. But now in 15w45a. I know you "solved", but i tested again and continue working. But to pass trought the blocks now is a bit harder. You need to shift 2 times now. Its the same mode to do this bug.

1. Be in creative mode
2. Make a roof with 4 blocks height of the ground
3. Fly and hit the head in the roof
4. Don't move it. Only for up and down.
5. Start sneak and fly in the same time
6. You gonna be stuck in the air.
7. But now, stop sneaking.
8. You gonna make your head go into the block. Like sufocating.
9. Stop pressing space.
10. Press shift with space.
11. Now realese the shift.
12. Now you pass trought it!