Found a bug in xfwm4 in both 4.8 and 4.10, if you set the button layout to "" xfwm4 segfaults like so
xfconf-query -c xfwm4 -p /general/button_layout -s ""
You can also set it to the empty string via the settings editor which does the same.
Using xfconf-query -c xfwm4 -p /general/button_layout -s "|" is the minimum it needs.
Not urgent but annoying.
Tried posting this on the mailing list but it got kicked back don't know why I'm sure I was subscribed, mods feel free to move this post.
The best place to report a bug would be: https://bugzilla.xfce.org/.