I’ve tried this on a page where the only plugin installed is GP Premium – the issue does still exist. :s
I can sometimes get “Backgrounds” to work by randomly activating/deactivating other features. However I can only customize my page once then. When I try to access “customize” again it shows me the white screen again. It’s just really odd.
I will try WP Debug and checking the error_log next. Let’s see if any of that works 😮