Too many network errors

I run "indexer -N4" daily, and quite frequently see this turning up in my logs 
-- a server stops responding, and gives an error message similar to this:

{01} Too many network errors (17) for this server

At the moment, this error has been repeating for the last 90 minutes, on all 
four threads that I run, for the same domain name.  My understanding was that 
when MaxNetErrors is exceeded, mnogo would move on to a new domain name and come 
back to this one later.  I have thousands of domain names listed, and 1.8million 
pages still waiting to be indexed, so why is mnogo so determined to get stuck on 
this particular website day after day?