I would venture this is a potential defect, if you are not running the latest SR of the major point release you are using, I would recommend doing and update to that SR and retesting to be sure it has not already been addressed there prior to reporting the issue via a support case. Here is the Help info on that feature:
The columns should adjust to the largest item in each column, including headers, so something does not appear to be working correctly in your case...
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