The UI not responding to resolution changes is a known missing feature. I don't consider this a major issue, as you can quit and restart in the new resolution to resize the subscreens. The sidepanel can be dragged around without a restart, though.
The lack of numpad key support is apparently an issue with the input library: https://sourceforge.net/tracker/?func=d ... tid=544942
that is marked Won't Fix by tzlaine. Essentially, there's no way to tell if numlock is activated.
The lack of alt-tab is presumably an issue with Ogre and possibly not something we can easily fix, so if you want to alt-tab, run in a window. At least on Windows, you should be able to switch between windowed and full screen without restarting, and if you set the windowed resolution nearly equal to the fullscreen resolution, the UI non-updating layout issues will be minor.