Only 20 users are displayed

Summary

Only 20 users are displayed in add new member drop-down combo-box.

Steps to reproduce

Create new project or group, go to 'members' page and open drop-down combo-box.

What is the current bug behavior?

(What actually happens)

What is the expected correct behavior?

I'd like to see all users in drop-down combobox. Or better - when I scroll down the list, the additional users are displayed. Or more better - make the configuration option which will control this settings (show only XX users or download the list dynamically)