I wondered if it was a bug. I know it did used to work and give a reference number. Nice to know that things that worked before have broken.... 
Did it ever work?
When Karlee was one of the first to try the IHS in 2015 as an AF dependant, UKVI told her to apply for her IHS under a category that didn't have to pay, which back then was Tier 2 (ICT), Aussie or Kiwi: but now they all pay the IHS too.
The bug on people being told children didn't have to pay (when they do, unless they are a dependant of AF) came later.
