I have added second HDMI display via Settings - Display. Now if I log in with HDMI display disconnected, I see black screen or just wallpaper without the desktop. I have solved this by manually adding an entry for LVDS to ~/.config/xfce4/xfconf/xfce-perchannel-xml/displays.xml , but this must be handled properly when using GUI only.
Probably an issue with xfsettingsd (xfce4-settings). Can it be reproduced with Xfce 4.12?
Closing old bugreports