Comment 2 for bug 912777

Problem caused by Brasero sending progress value = -1 in the initial stage of burning. The value of -1 is used internally by Brasero to indicate preparation stage or failure when burning; it's just passed "as is" to unity_launcher_entry_set_progress function.

We can fix the call to unity_launcher_entry_set_progress in Brasero to never pass -1. We could also add bounds check in unity2d - libunity-2d-private Application::updateOverlaysState method. But I think it's best to add bounds check (0.0 ... 1.0) in progress setter in libunity.