Fails to open full screen in Windows 10 tablet mode
1. Enable "Tablet Mode" on Windows 10, either the "original" August 2015 release and the new Anniversary Update.
2. Launch Calibre
Note that the Calibre UI does not fill the screen as it should. The fraction occupied varies depending on display size. It seems that there is some fixed pixel size. On my Dell Venue 8 Pro (1280x800) it fills the 800px dimension but only occupies about 2/3 of the 1280 when in landscape mode. On my deskop monitor at 1920x1080 it fills about 1/4 of the area at the center.
3. After launching (and grumbling at the overly small display), click the Minimize icon. In Tablet Mode this returns you to the Start Screen.
4. Click the Task View icon (the Win10 graphical equivalent of the old Alt-Tab) to display thumbnails of running apps and programs.
5. Click on the Calibre thumbnail and Calibre now fills the whole display properly.
Its is not a critical failure as there is an adequate workaround, but is rather annoying. I've documented it on two machines, a Dell Venue 8 Pro (32bit OS and 32bit Calibre) and a Dell XPS 8700 with AMD Radeon HD 7500 series gpu (64bit OS and 64bit Calibre). The bug has been present for the for a long time (>12 months)
This may be related to the old behavior (Pentium 4 based WinXP machine long ago) of opening a smallish empty window initially and then populating that window with the UI and resizing to the last used size.