Hello!
This changeset created a bunch of multipolygons (e.g. https://www.openstreetmap.org/relation/17605455, https://www.openstreetmap.org/relation/17605456) for the objects that were already marked as simple polygons. These didn't have any unusual geometries (as in https://wiki.openstreetmap.org/wiki/Relation:multipolygon#Examples_in_XML) to justify use of multipolygons. In this scenario converting simple ways to relations with many members just complicates further editing, as the features cannot be that easily separated.
What are your intentions with converting simple polygons to multipolygons? 