I am trying to add a ring in a feature in a shapefile. This feature is a single part feature but has already a few rings. When I try to add the new ring, I have the error message : "The inserted Ring is not contained in a feature". I tried to modify my snapping options thinking that the problem came from this setting, but I didn't have any luck.
Does anybody know how I can fix this problem?
I use QGis 1.8.0-Lisboa and Windows 7.