QGIS » QGIS Application

tested on qgis trunk under linux.

a) open a polygon shape, choose a polygon and add a ring with the proper tool. Toggle editing to save changes. The ring is not more a ring, it become a "part". In fact, if you want to remove the just created ring/part, you need to use the "delete part" tool instead of the "delete ring" tool.

b) Select a polygon and try add a "part" that overlaps the selected polygon, you'll get the message "New polygon ring not disjoint with existing polygons" and the "part" in not added, but the "island added" action always appear in the "Undo/Redo" stack.

c) For sake of consistency the "island added/delete" text in the undo/redo stack should become "part added/deleted"

d) After all it seems that "parts" that do overlap with the main polygon can exist (see http://gis-lab.info/share/10m-urban-area.zip and the above bug), so, considered that qgis does not allow create such geometry, we should always consider these layers as incorrect? After all (for example) the "urban area" layer returns many errors when its geometry is checked.

It doesn't seems to happen with postgis or spatialite, just shapes, BUT, if you create a ring in a postgis/SL polygon, then you save it as shapefile and then add it to the canvas, instead of the ring you'll see a part.