If you've got the same coated bridge as I do - there have been articles on the softness of the finish and it can rub off - especially if you rub it hard trying to clean it with any sort of abrasive polish or wax.
The white stuff is prolly an oxide from the metals in the casting and it may be telling you a bad pH condition that's leaching chemicals or metals out of the bridge.
Once the finish surface is broken - it's a short trip to new bridge land.
I'd go to the
Ibanez Forum and ask there - I've seen the factory dudes (they actually moderate the forum) on there do some interesting things for complaints like this.