Some usernames with special characters display without links in preview mode

Pre-conditions: register and activate user with usernames from attached file (usernames.txt):

Steps to reproduce:
1. Login jcommune with user which have permission to create posts.
2. Go to any topic and click "answer".
3. Enter the text from attached file (usernames.txt) in the text field and click "preview".

AR: Usernames shown as a text in preview mode(see first screen).
ER: On preview page usernames become links to the user profiles.

Note, that this usernames become links after creating a post