Multi Select List Box Document Property with Search bar enabled

Hi All,

I am working on Multi Select List Box document property with search field. 

It works fine when I give any keyword like 'An' it gives me Andorra, Angola, Anguilla etc. I can multi-select all these 3 records and make my underlying data table filtered.

Now the challenge is, if I search for the records that starts with in the search bar and click Enter then the above selection is deselected/disappeared (meaning the last search elements alone will be available).

Any ideas on how to make the current selection and newly searched elements available ?

Any inputs and suggestions would be much helpful.

Attached the sample dxp file and screenshots.