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Thank you for reporting this issue. Could you please provide the following additional details?
1) Version of Tableau Desktop in use when issue encountered?
2) Please verify the issue persists on the most current version (check here for the most recent version of Tableau Desktop).
3) If the issue persists with the most recent version of Tableau desktop, could you supply either a sample workbook (.twbx) here that displays this condition on a worksheet to explore further?
This doesn't seem correct and I cannot figure out how to reproduce your problem. Can you provide more details?