What engine version are you working in where you’re seeing this behavior? Do you see the same thing happen in 4.6 as well? Where in the editor where you editing the projection matrix value (inside blueprints, material editor, etc.). Any information you can provide that will allow us to reproduce this effect will help track down the cause.
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He was probably trying to do it as described here so extending UGameViewportClient and overriding Draw. Also please look at this thread. He also posted there, that’s why I think he tried the same technique.
Any kind of tutorial or an additional hint to get off-axis projection would be very helpful for quite a few of us.