Wrong result in (sub)totals matrix

I have a matrix view with some category on rows and year-quarter on columns. I use a live connection to and MDX cube and setup the time dimension correctly (including year-quarter). My measure calculates YTD () value.
Values are shown correct on rows for each category but not on (sub)totals rows when I select just one quarter via a slicer. The values shown on (sub)totals are the in period values (so not the ytd-value).
When I select 2 or more quarters via the slicer the (sub)totals are shown correctly.
Excel always shows the correct (sub)totals.

Please fix this issue.