I am new to the forum and to MFT, although I was an early adopter of the long-discontinued 4/3 format years ago. I began my MFT experience with an impossible-to-resist deal on an open-box Olympus E-PL5, complete with manufacturer warranty. As a former store display model there was enough dust on the sensor and in the rear element of the 14-42mm R II lens, which was included, that I was forced to learn very quickly how to differentiate sensor from lens dust among other issues. Needless to say, I have learned my lesson about "open box" (demo) merchandise. But for now I have a new (to me) E-PL5 that I'm enjoying otherwise. Now, however, I have a bit of a mystery on my hands, one that I need to solve before my return window (end of this month) runs out. The first incident occurred when photographing a flower one evening with my separately purchased (and otherwise excellent) 40-150mm Olympus telephoto lens. (I had just purchased the lens and wanted to test it even though the light was far from ideal at the time.) Unknown to me, a brownish circular haze appeared in the background, and in successive shots this "blob" moves closer until it is smack in front of a yellow petal (1/249, F6.3, focal length 111). In the next image there's no trace of it. I chalked the blob up to a slow moving dust particle, but it was a bit spooky nonetheless to look at the progression of whatever this was as it moves closer to the camera and begins to come into focus before completely disappearing again. Fast forward roughly two weeks and while testing a brand new 14-42mm pancake lens, which was the retailer's replacement for the aforementioned 14-42mm R II kit lens, I snap two 1/800th second images at F5, 14mm focal length only to capture a thin, green trail heading down from the top of the image towards a dark brown patch in which there are no details, just a solid brown color. I have no explanation for the two back-to-back photos that display the same anomaly only tenths of a second apart (11:14:17 and 11:14:19). Photos of the same scene either before or after those don't exhibit a problem. I am aware of the phenomena where a sensor can overheat, which can cause the look of fog, haze or smoke but not sure if that is the case here. Does this look like something other-worldly or a sensor that's going haywire? Thanks for taking a look at these! Edit: I've probably added about 1,000 shutter activations to what was about ~400 on the camera to begin with (that's an estimate because I forgot to check shutter activations right away). So I guess the question is, would a sensor begin to go out in a very erratic way — behaving normally for hundreds of photos — only to exhibit an intermittent problem? Conversely, once a sensor has begun to fail would it be expected to mar the photos in each and every successive case?