If a page gets an attachment before wiki text then it gets created with no creator instead of the uploader of the attachment (or saver of the wiki content).
1. Go to http://URL/xwiki/bin/edit/Main/Test1?editor=attachments&
2. Add an attachment
3. Go to http://URL/xwiki/bin/edit/Main/Test1?editor=wiki&
4. Add some content and save
5. Check http://URL/xwiki/bin/view/Main/Test1?viewer=attributes&
You will find that the Creator attribute is empty. This does not happen if steps 1 & 2 are after step 4.