Thank you for providing the screenshots.
There is really an issue with the width of the resource columns, we'll research it but most probably the fix will not be included in the service pack.
As a workaround, I would suggest to change the grouping like this (set DateGroupDescription first):
in this way, the width of all the columns should be equal.
The other option is to set Width to the GroupHeaders using GroupHeaderStyleSelector, the approach is demonstrated here
We're sorry for the caused inconvenience.
the Telerik team
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