Suddenly my keyboard behaves rather strange. What happened?
When you use mouse actions to re-size view elements you have to press simultaneously the Shift and the Alt key. As long as you really move the mouse nothing happens.
However, pressing Shift-Alt without mouse movement switches the keyboard layout to another language, like from English to German or Chinese. Since your keyboard hardware is still the same pressing some keys may cause surprising output. If you observe this, press Shift-Alt again until you are back at the wanted keyboard language. The current keyboard layout is indicated on the right end of the Windows taskbar (EN for English, DE for German, …).