SSRS 2008: MDX Query and Dimension Properties

Hello all,

I'm building some MDX reports where I have to show some dimension properties in the report. An example for one of my MDX queries is:

select
[Measures].[Total Costs]on columns,
[Projects].[Project].members
DIMENSION PROPERTIES MEMBER_CAPTION, MEMBER_UNIQUE_NAME,
[Projects].[Project].[Coordinator],
[Projects].[Project].[Head]onrowsfrom ProPlan

If I preview this query in Visual Studio's query designer the resultset will contain columns for the Coordinator and Head attributes. But when previewing the report always the following warning messages are shown for both attributes:

[rsMissingFieldInDataSet] The dataset ‘Projects’ contains a definition for the Field ‘Head’. This field is missing from the returned result set from the data source.
[rsErrorReadingDataSetField] The dataset ‘Projects’ contains a definition for the Field ‘Head’. The data extension returned an error during reading the field. There is no data for the field at position 5.

Do you have any idea what could be the problem?
Visual Studio 2008 9.0.30729.1 SP, Microsoft SQL Server Reporting Services Designers Version 10.0.2799.0

One important thing to care about is that Projects is a parent/child dimension. With normal dimensions everything works fine. If the query designer didn't show the attribute columns I would accept it as a disadvantage of parent/child dimensions. But I don't understand why it is working in the query designer (and in Management Studio), but not at report execution.

Thanks in advance and best regards,
Gerald