I've been testing this new 3.20beta5 today with the 
following comments:

1.) after the mirror completes, there is a button that 
says "View Log File".  In 3.16-2 this button flashed 
if any errors were enountered.  I just mirrored a site 
and updated another in v3.20beta5 and the "View Log 
File" button didn't flash post-mirror, even though 
some new errors were recorded.

2.) I found the "new.txt" transfer logs.  Could they 
include the 'file type' returned by the server to more 
easily identify "broken servers"?
I hope I'm not becoming a bother with all these 
postings/comments/requests :)

Thanks,
  Haudy