Limewire Island?
 

When in leaf mode, why does Limewire reject all hosts except Limewire ones? Are we imprisoned on "Limewire island"?
Also most hosts don't stay around longer than an hour.

I don't know about ultrapeer behaviour, 'cause it won't switch to ultrapeer mode here (cable connection - version 2.8.5).

LimeWire will not reject connections from any Ultrapeer in leaf mode.

The instability of connections is something that will probably never be solverd but I don't think it has any noticeable effect if connections aren't dropped too frequently.