Comment 2 for bug 141628

The patch below (that will be part of kde 3.5.8) fixes the issue:

--- lockprocess.cc.orig 2007-09-26 21:39:57.000000000 +0200
+++ lockprocess.cc 2007-09-26 21:34:42.000000000 +0200
@@ -417,7 +417,7 @@
 {
     Visual* visual = CopyFromParent;
     XSetWindowAttributes attrs;
- int flags = 0;
+ int flags = CWOverrideRedirect;
 #ifdef HAVE_GLXCHOOSEVISUAL
     if( mOpenGLVisual )
     {
@@ -461,6 +461,8 @@
         }
     }
 #endif
+
+ attrs.override_redirect = 1;
     Window w = XCreateWindow( x11Display(), RootWindow( x11Display(), x11Screen()),
         x(), y(), width(), height(), 0, x11Depth(), InputOutput, visual, flags, &attrs );
     create( w );