[However once I find a "unpushable" host it stays unpushable - even if I do a new search and download or restart Gnucleus. In such cases I often have to switch to Gnotella to download the file.]

Hallo:

I tried if this bug 'crawls' here also, but it was not possible for me to reproduce it. Every unpushable host I found was unpushable with Gnotella too, but I fear this will not help you further, for a non-occurence is no proof. But I will try further, if I could reproduce it I will let you know.
Did you report this already at sourceforge bug report form? You said you have problems with the forum, if you have problems with the bug report form also I will report it for you, if you want.

I think the coordinator [swabby] will read this anyway, (he has joined recently, even as moderator :) so maybe it is already known...

Greetings....