For some reason, NPOI returns "A65535" instead of "F9" in Formula1 field inside data validation. I read all validations from sheet using sheet.GetDataValidations() method, and then analyze ValidationConstraint field for each validations. In a validation where a field numeric value should be less that F9, in Formula1 field I get value "A65535", and when I open data validations pane from excel I see "F9".
Did anyone experience similar behaviour? This happens both with xls and xlsx files.