Hi,
The promote button simply lists some copy+paste code for you to put on your website linking to your item, it doesn't affect your listing on our store pages in any way.
Regarding the newest list, when we approve an item this goes to the top of the list. Sometimes we approve >10 items in one go, which means some might not appear on this list. I'll be more concious of this in the future and not approve that many in one go any more.
Are you able to access the promote button OK? If anything is broken or not clear, feel free to email me personally on tom at scirra.
Tom