In the same week Filtering was legalised in NSW, WA announced an increase in a lot of penalties across the board, not that I'm complaining about it, I think it will be good to help "educate" some of the drivers on mobile phones, penalty rising from $250 to $400, points staying the same.
The bit I suspect targets motorcyclists filtering here, since we actually have no law regarding it, is:
Failure to keep a safe distance when overtaking a vehicle
Old Penalty: $100 2 demerit points
New Penalty: $400 4 demerit points