Occurs only at design mode when user releases key that has been pressed.
property OnKeyUp: TKeyEvent;
It is the same as standard TWinControl.OnKeyUp event.
Use the OnKeyUp event handler to provide special processing that occurs when a key is released. The OnKeyUp handler can respond to all keyboard keys, including function keys and keys combined with the Shift, Alt, and Ctrl keys.
See TWinControl.OnKeyUp for details