The TitlesMultiselectWidget adds any selected items as tags when constructing a new widget. As the accompanying comment states, this should be upstreamed to its parent, MenuTagMultiselectWidget, since other subclasses should also do this too. (Not doing this in the UsersMultiselectWidget is the cause of T243075#5829744.)
TitlesMW and UsersMW are in core, but MenuTagMW (the parent) is in OOUI.
Since a new version of OOUI will not be pulled through until a week after the next train, we should do the following, in order to avoid T243075#5829744 becoming an issue:
- Add selected items to the 'options' config in UsersMW (core)
- Add selected items to the 'options' config in MenuTagMW (OOUI)
- Remove the lines adding the selected items in TitlesMW and UsersMW, after OOUI is pulled through, since it's now done in the parent (core)