Its not a bug, actually its a modified implementation to enhance HC UI performance. If you are installing a click app for an existing website let say testing.com then just type " t " in the website field and HC will list all the websites starting with T character, or obviously you can type full website name as well.
There were different cases for example a reseller have thousand websites/webadmin/Sold plan etc etc and when reseller try to provision the service then panel were suppose to display all the existing accounts/website on same page, which took long time to list them or even it expire the HC session.
FYI: It is already mentioned in the build
release note Modified Implementation: UI changes for optimization of large number of users and websites listing on HC Panel interface. While adding any hosting services under a reseller for an existing webadmin now you may write webadmin name or first letter in the field and it will display the existing webadmin.