That must have been something specific to your PC setup. It has never worked that way on my PC. That is non standard behavior for keys.
A key is supposed to generate a single '1' when the key has been held down long enough to be recognized based on the debounce timer. The next '1' would be after the 'start of repetion' timer expires. Holding down a key will result in a 1, a pause, followed by 111111111111111.
Mice work differently. A mouse generates a down event and up event. A left click is a down and up with the proper timer. That way the application knows the difference between left click, double left click and grab and drag.
You can program non standard functionality in an application if you want to. For example, you could set left mouse button down to be - display cursor, zoon in for a shot. Left mouse button up - fire the shot, remove cursor and zoom out. More standard way of doing it would be - 'h' draws a weapon and display cursor, right mouse button down - zoom in. Release of the right mouse button zooms out. Left mouse click fires one round. Hold down the left mouse button for a burst.
Unless stated otherwise, all content in this post is My Personal Opinion.