Configure button doesn't get enabled when the model rig is set to humanoid

Steps to Repro:
1. Open attached project or Import humanoid model > project window > select model
2. Inspector > import settings > rig
3. change animation type to humanoid > apply > observe that configure button doesn't get enabled

Workaround:
1. Change avatar definition > copy from other avatar> create from this model
2. Hit apply > observe that configure button is now active

Occurring with:
2018.1.0b5, 2018.1.0b1

Working with:
2018.1.0a7, 2018.1.0a1, 2017.3.0p4

Environment:
Occurring on windows & Mac