That's very interesting. The client must be programmed to specifically ignore the default loopback address however not other "loopback" addresses in the 127.*.*.* address space. I wonder why they would program this in to the client. I'm sure there's a good reason that I'm just not aware of.
Also, 0.0.0.0 use to be the most common loopback address but is not supported by Windows.
Darrell Chapman