Thank you for writing back.
I have tested this locally and the rows are hidden when the GroupHeaderHeight is set to 0. I have tested this with the latest and the Q1 2015 SP1 versions and the results are the same. This is why I have attached my test project. Could you please check it and let me know how it differs from your real setup?
In addition could you please specify which previous version you have used?
Thank you in advance for your patience and cooperation.
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