Thank you for writing back.
I was able to reproduce the problem that you are facing with Windows8 theme. I have logged it in our Feedback Portal. You can track its progress, subscribe for status changes and add your vote/comment to it on the following link - Feedback Item.
I have also updated your Telerik points.
Currently, the possible solution that I can suggest is to adjust the DateTimePickerElement.MinSize
I hope this information helps. If you have any additional questions, please let me know.
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