Ductwork in Design Master HVAC can either be centered,¬†flat on the left side, or flat on the right side. See Inserting Eccentric Transitions for more information.
When the offset changes in the middle of the ductwork, the ductwork will look like this:
To prevent this, insert a transparent duct at the break where the offset changes. The transparent duct centerline is drawn in red in the following example.