That happens to me too...

"Hmm... Let's get that one!"
"Hey! It doesn't appear in the 'Downloads' box!"
"Let me get it again..."
You are already downloading **EDIT**!
"What? No!!!"

True... I was trying to download that song... Then I waited for all of my downloads to finish, then tried it again...

Downloading!!!

Try that...

If you have no other downloads, just, maybe, I don't know.