Custom Buttons Hover Not Working as Expected

I'd appreciate thoughts anyone might have on an issue I'm experiencing with custom buttons and hover states.

I used the built-in illustrated characters to create a custom button set. Each character has normal, hover, down, selected, and visited states.

The issue is, the hover state doesn't seem to be working as desired, and here's what happens when I launch the slide:

1) I hover over the first character, and the hover state shows. 2) I click the character, and it changes as expected to the selected state. 3) I hover over the second character, and the hover state shows. 4) I click the second button, it shows selected, and the first button shows visited, as expected.     5) Here's the problem: When I go back to hover over character 1 - nothing happens. No hover state shows. Clicking does produce the selected state, as expected.

Would appreciate help determining why the hover state does not seem to work on the second pass.

Thanks!