Creating tasks doesn't work?

Creating tasks doesn't work. There is xml in response, for example
<response><result>
<TaskDetails>
<TaskDetail>
<pcompletion></pcompletion>
<todolistitem_title><![CDATA[new task through api]]></todolistitem_title>
<todolistitem_id>15301e67103a37959bc71e6f273ec0741c5699de5e886561</todolistitem_id>
<priority>None</priority>
<iscompleted>false</iscompleted>
<Tasklist_id>15301e67103a37956e2974ab7fd72a8b551803d538d0273c</Tasklist_id>
</TaskDetail></TaskDetails></result><uri>/api/private/xml/task/add</uri></response>

It seems that there are no errors and task is created. But this task doesn't appear on list of tasks later.

Is it a bug?