How to merge column headers in Cube View 8.4 - MergeAndCenterColumnHeaders not working

Hi,

I'm using OneStream 8.2 and trying to merge 3 column headers (Forecast, Budget, Var) under one "|!Entity_Selection!|" header.

I've tried  Setting MergeAndCenterColumnHeaders = True in Column properties
The merged header is not appearing. 

Has anyone successfully merged column headers in version 8.4? What am I missing?

Thanks!
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