Obfuscated email addresses should not be sorted

STEPS TO REPRODUCE

1. Login as Admin
2. Create some users, each with different email address set to their profile (it's important that first letter of the address to be different)
3. Go to Administer Wiki > Mail > Advanced and set "Obfuscate Email Addresses" to Yes
4. Login as a simple user (not really relevant)
5. Go to Drawer > User Index and add "Email" field in LT by customize it (<server>/xwiki/bin/view/Main/UserDirectory?customize=true
6. In LT, try to sort the entries in Email column

EXPECTED RESULTS

The email addresses cannot be sorted, since they are obfuscated.

ACTUAL RESULTS

The email addresses can be sorted.

What I reproduced is that on XWiki 14.10.3 and 14.4.7 the results can be also filtered if the first few letters of the email address are typed, but on XWiki 15.0 they cannot, they can only be sorted.