kmix volume slider popup sometimes stuck

When clicking the kmix icon in systray, a small window with basically only volume slider appears. Normally, when clicking the icon a 2nd time or when clicking anywhere else, this small window disappears.
But sometimes that's not the case for me, that means the window just stays there, no matter what I do. The only way I found to get rid of it in that situation is to click the "mixer" button. Then the mixer window opens and the small volume window finally disappears.
I didn't yet find any pattern of when that occurs or how to reproduce, seems random.

ProblemType: Bug
Architecture: amd64
Date: Fri Feb 19 21:17:08 2010
DistroRelease: Ubuntu 9.10
ExecutablePath: /usr/bin/kdeinit4
InstallationMedia: Kubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
NonfreeKernelModules: nvidia
Package: kdelibs-bin 4:4.3.2-0ubuntu7.2
ProcEnviron:
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-19.56-generic
SourcePackage: kde4libs
Uname: Linux 2.6.31-19-generic x86_64
XsessionErrors:
 (firefox:2188): GLib-WARNING **: g_set_prgname() called multiple times
 (polkit-gnome-authentication-agent-1:2189): GLib-CRITICAL **: g_once_init_leave: assertion `initialization_value != 0' failed
 (npviewer.bin:2304): Gtk-WARNING **: /usr/lib/gtk-2.0/2.10.0/engines/libqtcurve.so: wrong ELF class: ELFCLASS64
 (.:5550): GLib-WARNING **: g_set_prgname() called multiple times