Situation happens when we add or edit entry, and during this edition we decide to change uploaded image. Every time when we select and upload new image for same field, the number of POST requests are doubled, so when we upload image first time there is one POST request, then when we decide to change it and upload new one, and there are performed 2 POST request, after next change 4, then 8 etc... This number raise until we save the form, after saving and editing entry, whole process start from the beginning.
It also multiply number of images which are uploaded to the temporary folder at the server.