That one was made specifically for a WIP animation challenge that PJ had a while back, you can find the challenge info by clicking on the ribbon.
I found another one for you here:
http://pixeljoint.com/pixelart/29735.htm
You should post the finished version on PJ, and link to the WIP animation in the description. WIPs aren't allowed in the gallery (see rule #2). WIP animations make it harder for people to spend time looking at the final work, so even if it were allowed, it would be better to have the WIP be separate from the finished piece.
Use the pencl icon under the art to upload any revision you may have then hit submit again.
The no WIP rule is just for true WIPs and on a case by case basis. WIPs that go on to show the final pixel are generally cool and added such as this one did.
This exception or bending of the rules has developed over time because PJers just love seeing progress WIPs.