Hello,
I am having this same issue with Category images only. No matter what is done, the category image does not update.
I can update Item images fine, but category images do not update.
I tried deleting the image, saving the category with no image, and then I selected the new image from the server and it still put the old image back. I'm using K2 v2.10.3
UPDATE: I loaded the site in a different browser and the new image shows. Seems to be a cache issue. Went back to the original browser, cleared cache and new image is now appearing.
Kind regards,
John