I think the problem is two-fold:

1st. Ultrapeers don't correctly forward upload requests. I say this because I have a lot of files shared and my upload slots are usually full, but until I get promoted to Ultrapeer myself, I rarely have more than 1 or 2 uploads going. Forcing Client mode didn't help (see 2nd problem, below).

2nd. Disabling Leaf mode doesn't recreate normal Client mode, e.g. you're still limited to one connection.

As a further question:
I assume that Ultrapeers cache the file-list of all clients, both Leafs and Clients. How does it learn of changes? Does it cache the sub-directory name, e.g. \Star Trek\ ?

If you added some kind of client-cache diagnostics, we could try to figure it out. I suspect there's some major bug floating around in the code that you haven't realized yet. If I had more time (and programming experience) I'd gladly dig into myself, but my time is better spent beta testing. Sorry!