In BirdsEyeFrameManager.update(), the exception handler on line 756
resets self.active_cameras to [] (a list), but it is initialized as
set() and compared as a set throughout the rest of the code.
Since set() \!= [] evaluates to True even though both are empty, the
next call to update_frame() will incorrectly detect a layout change
and trigger an unnecessary frame rebuild after every exception.
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