I am not sure if this is resolved, I ran into the same problem using the image widget. I loaded a PNG image through the widget and then one through the media library, when it loaded there was no background, but once I hit save, the white background appeared. I opened the widget and deleted the height and weight so nothing was left in both fields, hit saved and the white space was removed. Again, this was the image widget plugin I was using. I hope this helps, it was a quick resolution for me.