When selecting 'propagationTOs' as display attribute in user list, an empty list ('') is always shown.
This happens because the information contained in the propagationTOs attribute is actually shown when clicking on the leftmost icon on each user's row.
By clicking on such icon, in fact, a separate request is sent to the server to inquiry the status of the given user on all associated external resources.
This inquiry operation is quite heavy to be performed by default for all users shown, hence the corresponding propagationTOs attribute is always empty by default.
Fix: don't show 'propagationTOs' among available display attributes in user list.