Cannot filter on ListView

When I try to filter on an ListView, the system doesn't return any results. The problem is not related to a single module, but for every related content and search value. Here is an example:

When I now try to filter on a column (e.g. subject) the returning result is always empty:

I was already able to track down the problem a little bit. The query that was build has an wrong whre-condition:

SELECT ...
WHERE vtiger_crmentity.deleted = 0 
...
AND ( vtiger_activity.subject 'test') 
...

As you can see the in the condition "( vtiger_activity.subject 'test') " as like-operator is missing.

I was also able to find the related error message:

                     ADOConnection._Execute(SELECT CASE WHEN (vtiger_users.user_name not like '') THEN vtiger_users.userlabel ELSE vtiger_groups.groupname END AS user_name,..., false) % line 1295, file: adodb.inc.php
                  ADOConnection.Execute(SELECT CASE WHEN (vtiger_users.user_name not like '') THEN vtiger_users.userlabel ELSE vtiger_groups.groupname END AS user_name,...) % line  366, file: PearDatabase.php
               PearDatabase.pquery(SELECT CASE WHEN (vtiger_users.user_name not like '') THEN vtiger_users.userlabel ELSE vtiger_groups.groupname END AS user_name,..., null) % line  388, file: RelationListView.php
            Vtiger_RelationListView_Model.getEntries(Object:Vtiger_Paging_Model) % line   85, file: RelatedList.php
         Vtiger_RelatedList_View.process(Object:Vtiger_Request) % line  563, file: Detail.php

At the moment I'm trying to find the correct positin in the code where the where-condition is built.

Maybe someone can help.