Median() function doesn't work as expected.

HI

I hope anyone can actually help me to slove my problem.

I am creating a calculated member by using Median() function.

The calculated member is Median(Sample.SampleID.members, Value).

Sample and Material are two different dimensions, which are linked to Fact.Value.

As you can see the correct median value over 4 sampleID and 1 material should be 1.567.  However, the MDX median gives me 1.713. It seems like that MDX median function() ignores the first SampleID and only apply median to the rest 3 Samples.

Does anybody know the reason?