Filtering multidropdown default value with existing list of things

My problem is not located on the database but only in front.

I succeed to display the full options list with this method Multiselect drop down

But I need to filter this result with the options wich are already selected. The problem is in the compatibility between list of text and options when I try to filter.

The current user is not important, this feature must be the same and work for all the admins