I'm on a Moto E2, running Android 5.1.
When I click the up/down vote button in the app, it turns red (like it's supposed to), and the vote number goes up. However, shortly thereafter, the vote button turns back to its default color (although the vote number stays correct)
Not a huge bug, but probably not too hard to fix.
Note: when I refresh the page, everything goes back to normal, as it should - the vote button stays red, and the number is correct.