Problems applies at least to MagicDraw UML 17.1.
Case: one has a Property variable typed by an Interface in a managing Class and one wishes to indicate (when a factory is not used) which implementation Class is assigned to the variable (say on lazy instantiation).
IMPORTANT: this matter is only of concern when a managing class has knowledge of concrete implementation Classes assigned to its Interface variables (such as for a demonstration class choosing demonstration items), it does not apply when factories are used !