If lighting is enabled, zooming in darkens the screen; e.g. zooming in to a completely white area turns it gray.
We're moving bug trackers, so I've opened a bug on http://bugs.opencompositing.org/show_bug.cgi?id=1119 . Sorry for the inconvenience.
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.