I am looking at
   pkg/35152: graphics/png: distinfo is wrong

  I tested and it attempted to download over and over again.

  Each time saying:

    fetch: Unable to verify fetched file libpng-1.2.14.tar.bz2

  This is a different behaviour than we used to have.

I saw this too, and it's a bit scary.

  It used to fail the first time if checksum didn't match and would try next 
  mirror.

  I don't think I like this new behaviour. I am not sure when this 
  changed.... maybe in July.

This is somewhat a tough problem, since the approach has to be ok for
various combinations of network trouble, wrong distinfo, and bad
distfile.  But probably the system should only try once per mirror.