Special Characters in username prevents them from creating a new space/new page with the message "Your session has expired. Please reload the page to try again."

Summary

Users that contains specific special characters in the username will not be able to create any content in Confluence.

Steps to Reproduce

1. Install a vanilla Confluence 5.10.3
2. Add a new user. Name this user userhashtag#
   
3. Login as this user
4. Drop down from "Spaces" and clcik the "Create Space"

Expected Results

The space creation dialogue pops up

Actual Results

There is an error message displayed in the UI : "Your session has expired. Please reload the page to try again."

Nothing is in the logs

Notes

This issue has been observed with the following characters:

1. '#"
2. '/'
3. '?'

If users are being synchronized from an external directory like JIRA or LDAP that Confluence will successfully synchronize and create the user and allow the user to log in, but they will experience this bug.

Workaround

Edit the username to not contain any special characters