New Post: Unexpected data conversion

I found that some pattern of text is converted unexpectedly.
Why this happens ?

This is sample code.

            var wb = new XLWorkbook();
            var ws = wb.Worksheets.Add("New sheet");
            ws.Cell(1, 1).Value = "06S00055";

The "A1" cell shows "1980/6/1" in a result.
But when I created new workbook manually by Excel2013 and typed "06S00055" into "A1" cell, nothing happened.

"06S00055" is a serial number used in my company.
I tried other cases, and found the followings.

• xxS000yy is converted to date
• xx = month
• yy = year (1925 + yy)
• day = 1