This was such a fun bug. It's fixed as of the next beta update so anything version 1.0.53 and above.
What was happening here is that most of our views (Activities / Fragments) have the concept of current site, and when the "Ask Question" page was opening it checked if the last view was site specific, and if it was got the site value from it. Since the achievements view is a global one, the page was finding nothing for the current site and using the default.
The achievements page is no longer considered a first-class view on phones (it never was on tablets since it's a real pop-up there, not a slide-in page takeover) and all of the logic for get-current-site now works via the view behind it, rather than checking against the achievements page itself. This also has the nice benefit of not getting rid of the site's logo in the action bar when you're viewing a question or something and decide to check your reputation changes.