Last modified: 2014-08-12 13:57:43 UTC
https://commons.wikimedia.org/w/index.php?title=Commons:Upload_Wizard_feedback&diff=prev&oldid=119805560 https://commons.wikimedia.org/w/index.php?title=Commons:Upload_help&oldid=119998385#Upload_wizard_doesn.27t_get_past_.27describe.27_section
Not only applicable when uploading PNGs. It happens to me all the time while uploading JPEGs. Size of the images may contribute to the problem though.
Katie, do the files also have big descriptions? Can you provide us with a log of any API requests that UW makes in these cases? Or an example image that causes the problem?
How about seeing a video? See <http://www.ktchan.info/files/wiki/bug64698.mp4>