You don't have to go to a sub panel to have the problem you are thinking about, it happens between the service disconnect and the meter.If you directly connect a sub panel to your main panel with a nipple. Dose it become part of the panel, therefore having common bonding and neutral as the main panel?
No, whether it's a 1" long nipple or at the end of a conduit run 100' away it's still a sub-panel because it is fed by a feeder. Now if your conductors were tapped on the line side of the service disconnect in the service you would have something different.If you directly connect a sub panel to your main panel with a nipple. Dose it become part of the panel, therefore having common bonding and neutral as the main panel?