I love this, but it does not seem to conform to standard UX best practices.

If I click and hold then move the mouse away to release, I assume an element should not register that as a click. As-is, this is inconsistent: the button registers a click, the checkbox does not.

I always had this issue when working with Flash developers. A common mantra was "don't reimplement scrollbars unless you can implement all the features a scrollbar comes with." They always had to do more than five iterations and spent days on that scrollbar.

Good catch. I've updated the button logic. The click will no longer trigger if the cursor is outside the button boundary.