This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
See UDN thread. Can we check HasUserFocusedDescendants() so we don't flush keys when the focus is still inside the viewport?
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-27565 in the post.