I am using QGis version 2.2.0 and I set the snapping option to the vertex, with a tolerance of 1.5 meter. When I draw a new polygon next to an old one, it seems like the vertices are automatically anchored to each other, but actually when I zoom in to a scale of, let's say, 50:1, I can clearly see that the two vertices have not been anchored. Instead of one single vertex, I have then two of them.
It's very annoying because this automatic error can create topological problems of overlapping and gaps among polygons. In fact I detect these problems when I use the topology checker.
Did you encounter the same issue? How can I avoid it?