When you initially place a drainage node you can use civil accudraw to establish a horizontal constraint that links the drainage node with the station and offset of the alignment. This constraint is stored in the node properties under Geometry point. If you don't use accudraw or if you drag and move the node you lose the constraint. There doesn't appear to be a way to re-establish this constraint. You and associate the node with the alignment but you lose the ability to move the node with hand coded entries. There should be a way to add this constraint.