Bottom Line-
ANY TIME you see a gray screen after you click "Reply" or "Go Advanced", Look at the bottom line for a SCROLL Bar.
When a post contains a very large pic, the software resizes it to a reasonable size for viewing in the thread.
However, if you click "Post Reply" or "Go Advanced" on the Quick Reply window, the large pics revert to full size and you must look for the Scroll Bar at the bottom of the page.
I posted a large pic here that reverts to the large size and creates the Scroll Bar at bottom.
Try It. Click "Post Reply" or "Go Advanced"--------
Photo courtesy of
RKmesa