standing atop a boat sitting atop a second boat in multiplayer gets you kicked for 'flying is not allowed on this server'

In SMP, place a boat, then place a block near it and place another boat atop the block. Get in the upper boat, and pilot it until it rests atop the lower boat. Get out of the boat. Jump on top so you're standing atop the boat pile. (See screenshot)

Expected: stay on the server
Actual: get kicked for flying