I just posted a dupe, sorry about that.
The reason however was because of loading time of the submission checker. It returned 0 shots for the movie, which i already thought was suspicious and even tried opening it in IE (chrome still not that standard i guess) but it still didn't load anything.

Later when i saw my submission deleted i noticed IE was still open on the check page, and guess what...a lot of images had appeared including the one i duped.

Maybe a warning should be placed on the page? Or maybe print the total number of pictures first before displaying them, so the user knows for how many shots to wait. In my case it did show the curtains, but no shots inside (not even unloadable images, which i got when posting my latest shot after that).
Maybe even better to only activate the buttons if all shots are displayed, but i guess this is harder to check/implement.