When recording multipolygons, the individual ways contained in the multipolygon as outer-, or inner- segments must be arranged in the correct order. If that will be correct, the relation editor in JOSM shows a closed rectangle in which all related ways are located. 
https://josm.openstreetmap.de/wiki/Help/Action/CreateMultipolygon

Ways are defined as vectors in OSM and therefore have a “direction”. It is always good for subsequent processing if the individual ways, which together form a closed multipolygon outer line, all have the same direction. However, this is not possible when using ways that are assigned to several multipolygons at the same time. In addition, the isolated maintenance of individual polygons in OSM is made much more difficult.
The principle should always be Keep it small and simple