Cannot add user proxy.

Platform: http://folio-testing.aws.indexdata.com/

Path to failure:
1) Load users module
2) Click Active limiter
3) Choose a user from user list
4) Click edit icon (pencil) from detailed record
5) Expand Proxy/Sponsor section
6) Click +New to add a "proxy for"
7) Click Active limiter from modal window
8) Poof! The screen becomes white.