Currently auto-completer uses sync call to prepare auto-completer source (result list).
Due to this user can't perform any other operation on lookup field and user should have to wait until response came.
In general, synchronous requests should never be used because they tend to block the execution of anything else on the page (or even the entire browser UI), which isn't good.
Also ajax-loader image not display on google chrome browser due to sync request.
Need to use async request for auto-completer.