I get no summary values when using YTD in Analysis Studio

[BISandra]

In Cognos Analysis Studio (10.1), I get no summary values when using YTD (a calculated member, mdx-expression, in Microsoft Analysis Services cube 2008).

I use the time dimension nested with YTD as columns, quantity as a measure and I select two members from any other dimension as columns, for example product A and product B. I automatically get a summarized column in Analysis Studio that gives me the "--".
If I select the whole product hierarchy instead of two members, it works as intended and shows me a correct summary.

Has anyone encountered this problem before?

[CognosPaul]

I have run into this problem before, and it is incredibly aggravating.

Cognos is saying it doesn't know how to correctly roll up those two members. If you do Product A + Product B you will (should) get the correct result. To the best of my knowledge, there is no way to fix it.

[BISandra]

Paul, do you think this is a matter of how you wright the mdx (for the calculated member YTD)? Should I modify it in some way in order to handle multiselect differently?
I've logged a case at the support, I let you know if they have a solution for this.