Usernames with spaces do not work with page restriction auto-complete

When a username containing a space is selected from the list of auto-completion results in the page restriction dialog, a message like the following is displayed:

Unknown user or group: user+name

Entering the full username (including spaces) and hitting the "Restrict" button works as expected, this only happens when clicking the user in the auto-completion results.

Steps to reproduce:

1. Create a Crowd user whose username contains a space (such as "user name").
2. Log in to Confluence as that user and create a personal space.
3. Log out and log in as a different user
4. Edit a page
5. Start searching for the user by typing the word "name"
6. Click the full name for "user name" when it appears
7. An error message will appear

I don't know if this problem is reproducible with LDAP users.