Redirect to login when trying to search

We are using Confluence 5.9.3 and when an anonymous user tries to search when he is on the main page it will automatically redirect to the login form.

Steps to reproduce:

1. Open incognito tab
2. Visit http://my-xconfluence/
3. Click into the search area at the right top
4. Redirect to /login.action?os_destination=/

I've also attached a screenshot which is visible for a split second before the page is reloading.

The issue does not occur when searching from a space (using the same toolbar search field) or on the field on any not found page e.g. /not-existing-site