It may be a feature but just wanted to point this out.
I see the following behavior
uploading a PNG image with transparency through the browser (Safari 9.1 on OS X), the file is uploaded as a PNG with transparency
uploading the same file via the iOS app via the PHOTO icon at top results in the image being converted to JPG automatically, losing the transparency
uploading the same file via the iOS app but using the general “upload files” file picker, the image is uploaded as a PNG file with the transparency intact.
Is this an intended spec?