Bug#851399: Possible workaround

[Kethen Chui]

https://bugs.launchpad.net/ubuntu/+source/xubuntu-default-settings/+bug
/1431149/comments/14

Try removing light-locker and light-locker-settings package as the above link suggested, on suspend the xfce uses xscreensaver to lock instead without changing VT. Alternatively maybe you can find a way to configure xfce to use xscreensaver to lock on suspend, however I'm not too familiar with xfce so I guess you'll have to google, read docs or ask around.