[Qgis-user] can not display vector layers as "graduated" or "catogorized"

[Anders Siren]

I try to change the display of a shapefile vector layer from "single symbol" to "graduated" or "categorized", but when I do that, the whole vector layer disappears from the window. I then try to do "zoom to the extent of the layer", but it does not help, it just does not appear again, although the layer is still in the layer panel. I have tried on two different computers and with various shapefiles, and nothing helps. Is there a bug, or am I doing something wrong?

By the way, how can one report bugs? On the QGIS website I cannot find information about this.