When you have your WYSIWYG enabled and are uploading a image saved in Photoshop you will get into trouble.
Below you see a image with the problem;
I have only seen this happen with images saved in Photoshop. Any other program that I have tested does not create this problem. But if you see it with images save in other programms please let us know.
The solution is very simple. Just save the images that are giving you this problem in a different program than PhotoShop and you are homefree.