Just upgraded from 1.4.75 to 1.4.83 on Windows 8.1 64-bit, fully updated. GUI is now just a blank gray box. I've been using BTSync for about a year and a half, on almost every platform you support...Android, IOS, Linux, Windows...and things worked acceptably well up through 1.3.109, but the slew of problems I've had with 1.4 is making me nervous that I might lose important data. Your developers clearly aren't doing enough testing prior to release, and the problems I've had indicate this is equally true for the syncing code as the GUI. A bug that accidentally wipes out some part of the 5 TB of data I'm Sync'ing seems increasingly likely, and that is an unacceptable risk. Seriously, open source Sync so the community can help you fix the bugs! Or you will lose myself and I imagine a large portion of your users when an open source alternative arrives.