Oly C750 Light leakage?

Has anyone else taken long (10+ secs) shots at night and noticed that
there is a smear of light at the top left corner of the shot?

It looks like bleed from the viewfinder. But I placed the lense cap
on, took another 16 sec shot with the LCD on, and not the VF, and had
the same result!

Has anyone else struck this?

I am interested in whether it's a fault of the camera or my camera.

Thanks for any advice
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I was frightened by the idea of a conspiracy that was
causing it all.
But then I was terrified that maybe there was no plan,
really. Is this unpleasant mess all a mistake?