Calling DiscardPlayerInput() does not appear to actually discard the player input. The comment for the function indicates that input will be consumed and discarded without doing anything with it. However, when playing the game all input still appears to be applied normally.
All of the inputs are applied normally even though player inputs should be discarded.
All of the inputs are discarded and not applied.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-60809 in the post.