Error searching in custom field

Hi, if user is not Administrator and search in "searchbox" for custom fields, the system show an internal error:

Steps for reproduce:

1. Login to webissues demo:  https://demo.mimec.org/
2. Login with "demo1" and "demo1"
3. Select type: Tasks
4. In searchbox, change to "Priority"
5. Insert value "1" and hit enter or click in search icon.

The systemo show "Unexpected Error".

Regards!