I'm not seeing what you're seeing. When I go to upload a new avatar it lets me choose the file, save changes, and then it automatically changes. All I can think of is that you're trying to use a photo that is too big and it is asking you to crop.
If that is the case, it is asking you to drag and crop within the picture itself. What you would do is click somewhere within the picture and then a little box would appear (with flashing dash lines outlining the border of the box). You would manipulate that box to let the forum know what portion of the picture you want "cropped" down to their 200x200 standard (could be the whole picture, or just part of it...you decide).
Don't know if that'll help but could luck!