Version: (using KDE 4.0.80) Installed from: Debian testing/unstable Packages The calendar of the digital clock plasmoid is not visible if running X with nv driver. Only the frame is drawn, but not the calendar itself. This works fine with the nvidia driver, so I guess it has something to how the calendar interacts with desktop effects not being supported by the nv driver. Other plasmoids seem to work fine.
as you note, this is an x.org driver issue. nothing we can do about it. please report it upstream.