The calendar view in the task app is not able to be filtered. This has been raised previously and there is still not a fix available. can you please give an ETA for when the bug will be fixed?
Problem: SharePoint 2013 Enterprise: Create a task list, add a category column. Try to create a view with a filter on the category, nothing is filtered, everything still shows up in the calendar view.
Here is the previous forum question: http://social.technet.microsoft.com/Forums/sharepoint/en-US/53a7840c-5ffe-499e-933c-e93898beee54/sharepoint-server-2013-tasks-views-calendar-views-filtering-problem?forum=sharepointgeneral