Project browser creates nested scroll bars when you have a lot of projects
1. Launch UE4Editor.exe with no project selected
2. Attempt to use the scroll bar next to "My Projects" or "Samples"
Result: You'll see it expand immediately creating nested scroll bars. The interior one will disappear, but the effect is unexpected. Overall these self-expanding sections feel a bit clunky
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-29483 in the post.