All sculpting used to disappear before. Save MDISPS if new mesh has got the same faces amount. NOTE: maybe some other layers should be saved? - Apply multires modififier if MDISPS was auto-created. Multires's applyModifier used to return unchanged DM when MDISPS was auto-created. - Set multires totlvl from MDISPS layer when new multires was added to mesh with existing MDISPS layer.