That's odd that you have the same bug right out of the gate on two different devices. I've not experienced anything like that, so not sure what it could be. Did you try using it on the V20 before downloading your books? I ask because I'm wondering if one of them is somehow causing things to act up. It wouldn't hurt to use the app manager to clear the app data, then try using it without re-downloading your books to see if the problem persists.
If you haven't already, I'd try contacting their tech support and give them all the details. They would know better than any of us what could be going on.