Any possibility that either the Mini or Roamio has an extra network going on it (that might give you the symptoms you see)? Are you sure neither has wireless connectivity? (There's a bug with the Roamio that it is tough to turn wireless off if it was ever set up with it.) Is there only one of ethernet or coaxial cable connected to the Mini?
TiVo Roamio:Felix TiVo Premiere:Bob TiVo XL4:Fred TiVo HDXL:Sharon TiVoHD:Susan