There is one condition to see this bug: user must have invalid session settings.
You can set "Xsession" key to invalid value in /var/lib/AccountsService/users/<username> file.
Or you can delete this file, greeter will use value provided by lightdm_greeter_get_default_session_hint(). This value can be invalid in some dists (in Arch it is "default" - there is no real session with name "default").
There is one condition to see this bug: user must have invalid session settings. AccountsService /users/ <username> file. greeter_ get_default_ session_ hint(). This value can be invalid in some dists (in Arch it is "default" - there is no real session with name "default").
You can set "Xsession" key to invalid value in /var/lib/
Or you can delete this file, greeter will use value provided by lightdm_
What dist are you using? 51% it is not Ubuntu.
Provided branch must fix this bug.