I noticed there is a problem with some of the pictures taken with Mamiya RB67 + 65mm f4.5 lens. You can see a brighter spot of light almost in the middle of the image (it almost looks like a smoke). This happens only in situations when the subject is quite dark but the background is very bright (please see attached photographs). I went to the camera repair shop. They said it's not caused by a light leak. It's usually the problem with the lens (some mold) but they checked it and it had no problems. I've read that when using UV filters (mine is not very expensive) there can be some flares occuring on the images. Could that be the problem? Has anyone ever experienced something similar? Could you kindly help me to solve this issue? Thank you very much!