Mint 19 xfce (updated):

To replicate:

    Create user in 'Users' app
    Log into new user
    Log out
    Log into old user
    Delete new user in 'Users' app
    Log out

Expectation:
New user login will be gone.

What happens:
New user login is still visible.

Fix:
Reboot computer before deleting new user.

Version:
Unsure. I get:
$ Xfce4-session --version
Command 'Xfce4-session' not found

$ xfce4-about
Command 'xfce4-about' not found

$ xfce4-panel --version
xfce4-panel 4.12.2 (Xfce 4.12)