Maybe you will observe a changed mouse and keyboard behaviour after updating X.org recently in Debian Sid. Then you will probably discover the warning mentioned in the title in your X.org server log /var/log/Xorg.0.log. The very short and dirty solution to get things working for the moment is to put this into your /etc/X11/xorg.conf:
Section "ServerLayout" Option "AutoAddDevices" "off" EndSection
See the first entry in /usr/share/doc/xserver-xorg/NEWS.Debian.gz and follow the mentioned links for more information. However, the above solution should only be a temporary workaround: Try to migrate things (I will post changes for my system asap).