When I work in QGIS and try to fill gaps between polygons creating another one over them (project snapping settings are selected as Avoid intersection), I hope "fill" this gap with just one polygon with the same shape, but sometimes when I create this polygon I create a multipart polygon, which contains the principal polygon and some segments of 2-3 vertex, most of them, between other polygons created and where there are not gaps. Why does it happen, if snapping setting must avoid it?