When shift-building a bridge into a spawn-protected area, you will fall down when the server removes the placed block. You should never fall down when shifting.

I have been playing custom PvP maps, which often have spawn-protected zones, and have meet this problem often .

Perhaps the info about which zones are build-protected could be duplicated on the client?

Demo video: http://youtu.be/GixdV7PvtKI