WPF KeyBinding swallowing keys, preventing TextBox use

I have the same problem. I took a look to documentation for key bindind, and there is described, that the key on which you bind shouldn't be just key, but key gesture, so it shall be

• Modifier key + normal key
• Numeric keypad key
• Functional key.

Of course, it works with just A, but it's bad practice overall. You should consider to implement some of the posibilities mentioned behind. More at https://msdn.microsoft.com/cs-cz/library/system.windows.input.keybinding(v=vs.110).aspx