Version 5.4.0b15 Build #2016041801 (unity-editor-5.4.0b15+20160418_amd64.deb)
Unity consistently crashes when clicking outside of various popups (Material Selector, Color Picker, Animation Add Property, Animator Layer Properties, Physics Material Selector, etc.).
Not a deal breaker but highly annoying to have your whole project crash when mis-clicking somewhere.
Ubuntu 16.04, latest Nvidia drivers (361.42) on GeForce GTX 950, 8 Gigs of RAM.
Simple test project screenshot illustrating issue: