MouseDown behavior

[cursor]

To understand mousedown behavior in a simplistic dropdown menu, I created a small model. (See attached .web file.)

• All buttons and dropdowns have 1) mouseOff, 2) mouseOver, and 3) mouseDown states
• All links = javascript:;

I note the following behaviors:

• The button 2 (no dropdown) can be pressed any number of times and the mouseDown state functions properly.
• The button 1 (with dropdown) can be pressed exactly once and the mouseDown state functions properly. If I press the button multiple times, with the cursor in exactly the same position (no hand/mouse movement), only the first click behaves as expected. If I press button 2 multiple times, but ensure that the cursor moves before each click (even if only slightly), then the mouseDown function works properly.

Why does button 2 (on popup layer 'btn1') behave differently?
What are your observations?