I recently had version 3.3.4 and had this problem. I realized I was on an old version and upgraded to 3.4.1 but the problem hasn't gone away.
Compare the two pictures attached. I used FTP Upload to add it. However, I have uploaded via Drag'n'drop and it does the same thing. The "Bad" image is what I get when I click the little "download" icon when viewing the image or in the category list view. If I FTP to the server, browse to the folder, and download the image. I get the "good" version. So, the image on the server itself is just fine. Something happens during the download process that is re-creating the image and ruining the picture.