While in gamemode 3 (spectator mode), you can noclip inside the barrier block with no problem. If you switch to gamemode 0, 1, or 2 (survival, creative, or adventure) while inside the block, the game will crash. Happened for myself on Win 8 and my friend on Win XP both on my self-hosted 14w05a vanilla server. Also occurs for both of us in Single Player worlds. Does not occur with only feet in the block, then you will simply be shoved until not standing in a barrier. Will occur if head is in barrier and feet are not.