(I know it is not obvious, but issues with download.o.o is strictly speaking is not part of buildservice@ list.
It is better to have this config in heroes@ or mirrors@ list, but I may be wrong).
Strict answer to your question: the difference is that Tumbleweed redirects to *Snapshot* first, because of some Apache magic. And Leap redirects to MirrorCache right away. (And MirrorCache has harder time to handle symlinks properly).
But there is a change in MirrorCache behavior planned for this Thursday, so it will never try to serve *Current* and similar symlinks directly, but instead - it will try to always redirect to corresponding Build or Snapshot files.
Let's stay tuned and see behavior on Friday if everything goes well.