strange keyboard behavior on screensave

Running KDE47. When I leave the computer for a sufficient time to let the screen saver kick in, a shake of the mouse reveals the basic login dialog with no background. If I attempt to enter my password into the field, no characters appear and the login fails. However, if I do a Ctl-Alt-Bspace, X is restarted and the full background pic is displayed along with the log in dialog, and it will accept keyboard entry... Ideas, anyone? -- Claude Jones Brunswick, MD, USA