I was able to go around the glitch by uploading a picture one at a time. Try this:
On your web browser open three tabs and put them on planet minecraft. On your first tab, begin your post by uploading a picture. It won't show anything but once the uploading icon has finished, close that tab. Go to the next tab and pretend to start all over again. Your first image should still be there. Upload your second now. Rinse and repeat with as many tabs as you need (tabs for the speed if you have a bunch of photos). Hope this works for you.
