Window placement

[Marshall Neill]

I have noticed over the past couple of days that the Window Manager 
Tweak for Centering Windows stopped working.
If I reset/change the setting it will work for a while then stop centering.
I checked all my updates and there was no indication of an upgrade of 
any Xfce packages, least not directly named as such.
I am running on Debian Sid (Unstable) and this is the only problem I 
have encountered.
I checked permissions on the xfconf directory in .config and all 
subsequent permissions and all are correct.  Just checked to make sure. 
I really didn't think that was the problem though.
I checked in .config/xfce4/xfconf/xfce-perchannel-xml/xfwm4.xml and it is:

     <property name="placement_mode" type="string" value="center"/>

I have moved the slider, in the Placement tab of Window Manager Tweaks, 
from Small to Large and still the same problem.
So everything appears to be right but not working consistently.
I have Compton as my Compositor but have been using that for over 2 
weeks with no problems.
Any ideas?