Small PNGs changed to jpgs when uploaded, even retroactively

Hey! Recently, imgur started uploading all my pngs as jpegs (adding the jpeg artifacts) while leaving the file extension the same. This happens not only on small images (like http://i.imgur.com/9d6OZiu.png - you can see the lossiness, and it wasn't even close to 1MB) but also to OLDER images which were previously lossless after upload (such as http://i.imgur.com/HxIDdK0.png which was many months ago a 16KB file that uploaded lossless). What's the deal? How do I start uploading lossless PNGs again?