Application may freeze when offline

Version 1.2.0 on Windows 10, offline

1. Entered title and author.
2. Uploaded a JPEG cover (~28k size). -> image showed up.
3. Clicked on the cover. -> Program window became blank. No widgets. Mouse "Back" button not working. 
4. Aborted by closing the window via the top right "x" button. 
5. After restart, the book was still there, but no way to edit it. This is reproducible. 