All teams do it at all times. As has been said it's something that the ICC should've sorted before now to be honest. I reckon only about 1/4 times the 12th man comes on is for a genuine reason, so for me like a 4th official in football, an official should be on the boundary to determine if the 12th man can go on, avoiding cases like yesterday with the Pak 12th man getting to the wicket for the ump to send him straight back. By going on the pitch he's still done his job, stopping him stepping over the boundary rope will reduce some time wasting. That and they need to actually be strict with over rates, I don't think I have actually seen a team get penalized runs for it, despite the rate rarely being achieved.