Visited vs Selected state
I know Visited vs Selected states has been discussed before, but in researching an issue I was having, I made an observation that doesn't seem to have been brought up before and I thought it might be helpful to somebody.
When a button is selected, Storyline shows both the Visited state and the Selected state - it does not switch between the two states. Contrary to what you might expect, the Visited state takes precedence over the Selected state - that is, the objects in your Visited state are displayed higher in the Z order than objects in your Selected state. So if you have an object like a green rectangle as part of your Visited state, and a blue rectangle as part of your Selected state, and you position those rectangles in the same position, you will never see the blue Selected state rectangle: it will always be underneath the green Visited state rectangle.
My workaround is to separate the two indicators - I now have the Visited state indicator on the left side of the button and the Visited state indicator on the right side, but it would be much cleaner if I could have them stacked. If Storyline reversed the Z order of those two states, then it would work as you might expect it to - Visited state indicators would appear as appropriate, and the currently-selected button's Selected state indicator would appear on top of the Visited state of that button, making the sleected button look, well, selected.
Hope this helps someone.