Visited vs Disabled

I was playing with something today after watching a video, and ran into something that i hadn't noticed before.

I created the attached slide.  The idea was to change the state of the character to either visited or disabled, depending on which button they pushed.

Both buttons changed the state as planned, but if you clicked on the visited button first, then the disabled button wouldn't change the state to disabled.  However, if you did it the other way around (click the disabled button first, then the visited), it would switch.

I created a third button and a new state - Test 1.  I could switch between visited and test 1 all day long. 

So, i'm just curious - what is it about this relationship between Visited & Disabled states that keeps you from going from V to D?