When creating a partial discharge of mortgage (or encumbrance etc) in the context of a boundary adjustment dealing, if only part of the land in a title affected by the mortgage is to be discharged (ie the part being transferred to the adjoining owner), you must select the Part of Land/Complex mode and enter the description of the part affected.
If you do not select Part of Land/Complex mode then the mortgage will be discharged as to all of the affected title (ie the title recorded on the Create Dealing screen).
If this were to occur by mistake, the certifying lawyer would be responsible for the consequences, including any costs associated with having further mortgage documentation registered to rectify the matter.