I started using WAB 1.3 last week, and I have had nothing but problems with the "Previews" panel that simulates the sizes of various screens.
At first it would freeze/crash, or disable the "Save" button, but just now it reverted my entire app back to the initial configuration (which was basically no configuration). I checked the app folder in the server\apps directory to verify it was gone, and sure enough, all the other widgets I had added were gone, etc. Just lost and overwritten.
I could not find any other information/discussions about this. I am not sure if it is a bug with WAB 1.3 or an issue with Windows 8.1 or something else. I have already started my app over on a different computer, and I am saving my text files (disclaimer, help text) in Word documents in case something like this happens again. I am just sad for losing so much time