I've had the same problem
After a certain size they get converted. Just make them smaller. See:
Use third party uploader.
http://www.imgur.com/https://catbox.moe/
For all your carefully cut out Anglins
It's just size. If the image is too big it's converted to a jpg.
It's a shame that discourse doesn't handle this similarly to imgur, which converts if the image surpasses the 1MB mark. I was confused because my image was so small in filesize.
Thanks for clearing it up.
