When trying to install the application, I get the normal "Do you want to install this application?" followed by the list of permissions required.
At the bottom, I can either "Cancel" the install, or proceed by pressing "Install".
Unfortunately, in my case, the "Install" "button", is not a button at all. It's a completely inactive text, and no matter if I tap it multiple times in different locations or long press it, it reacts in any way at all. Cancel works fine.
I've tried disabling the setting allowing installation from unknown sources and re-enabling it, and I've tried restarting the phone. Neither helped.
I've tried several of the humble bundle applications, and the issue is the same with all of them. Since the confirmation dialogue is a part of Android, I assume the issue is unrelated to Humble Bundle.