If you upload an image with transparency (for example PNG) in Pholio, it shows the transparent areas white in the preview area of edit view, but in the saved dialog it's shown on transparent checkerboard.
That's confusing and had me re-edit/-upload several mockups twice in recent weeks. Expected behaviour would be to see checkerboard already in the preview.
Original report: https://phabricator.wikimedia.org/T135285