Thanks Stu.
Somewhat related - and in the engine this time.
If a file has "Swap every A4AF to this file (auto)" enabled then a source host with"no needed parts" will be swapped to another file that it has parts for _only_ if that other file also has the option enabled.
IE: hosts with "no needed parts" can end up locked onto A4AF priority files even though they may have valid parts for other files being requested .
If I'm watching the source list for a file with A4AF priority set, and then disable the priority, those "no needed parts" sources are usually shifted to other files almost immediately.
I hope that makes sense...