Heimer Turrets

I was playing a game and the opposing team had a Hiemer and the last I check his turrets didn't target Towers and the towers pretty much one shot his turrets. Well This Hiemers turrets were firing at the turrets (Including the Ult powered one) and not dying in a single hit from towers. Is there something I missed in PNs or is this a bug that needs a swatter taken to it?