Next button will not return to state normal from disabled state

I am at a loss as to why this is not working. I have a slide with 3 buttons. Each have three states: Normal, Hover and Visited. I want the NEXT button on this slide to be disabled until all three have been visited. I can get the button to disable, but not get it to enable again.

Here is what I've tried.

First, I set the NEXT button to disabled when the timeline starts.

Second, I set the NEXT button to return to Normal when all three buttons have a state of Visited.

This didn't work. The button is disabled, but never re-enables.

 

Next I tried a True/False Variable and followed it exactly from the articulate support articles. Again, the button was disabled, but would not enable after all three buttons were visited.

 

Finally, I thought that I should assign a value of Visited to each of the buttons, so using the first model above, I added a trigger for each button that when it is clicked, a state of Visited is assigned.

Still - the button is disabled! Aaah, can someone please help!