Service Desk custom Email address not reflecting in Enable service desk page in UI

We have gitlab CE installed in a cloud hosted VM.

We want to enable service desk functionality. so we have configured incoming email address as incoming+{%key}@xxxx.xx and gitlab_rails['service_desk_email_address'] = "supportgitlab+%{key}@xxxx.xx".

After changing configuration we have restarted gitlab.

Issue: We enabled servicedesk by going to project -> Settings -> General -> Activate service Desk.

Here instead of showing supportgitlab Email address in "Forward external support email address to" field. it is showing incoming email address. which is strange.