I windsurfed at Mullaz a couple of times last season and was well outside the kiters area. Didn't see anyone shaking their fist at me so it must have been OK.
Much better spots to windsurf just up and down the coast anyway, so I don't think they have much of a problem with poleboarders. When I was there last Saturday I could only see signs saying "No kitesurfing" so I guess it's OK to windsurf there if you stay well away from the surf club and be respectful of other water users...
The Joondalup council rules address kitesurfing only. Windsurfers are not restricted to the same area. I have friends who windsurf at Mullas and they do not need to windsurf within the same launch/land zone. Lets hope the bureaucrats don't ban them as well.