The user is shown an "default" tool tip message when hovering the mouse over material parameters.
From UDN https://udn.unrealengine.com/s/question/0D54z00008CrEIGCA3/broken-material-layer-parameter-descriptions?fromCase=1
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-167024 in the post.