Any controller that I open with TTNavigator results in a blank view

I recently migrated an old project that uses Three20 from Xcode 3.2 to Xcode 4, and after the transition, some really weird behavior occurs whenever I launch the application: whatever is the controller I open with the navigator, a blank view is presented to the screen. The funny things is, I am able to touch the UI elements that are supposed to be there (for example, in this screenshot view I can tap a text field and the keyboard gets presented). Has anyone got any idea of what's happening here? Please note that I haven't changed a single line of code from the working old version: I just migrated the project with ttmodule.py.

The problem arisen because I forgot to remove the window outlet from my App Delegate (both in the interface declaration and in the XIB file). Since TTNavigator uses his own window to present view controllers (unless specified explicitly), creating another window can result in weird behaviors. Apparently, this didn't give any issues with the old Three20 (or maybe Xcode) so I didn't even notice.