We are working with v6.5 of the library and the JSS eclipse plugin.
When exporting using the method 'JRXlsMetadataExporter()', the property net.sf.jasperreports.export.xls.ignore.text.formatting does not work for an element where the markup is set to 'html'. The font size and type are kept for the cells in the exported xls file.
Changing the element to a markup of 'none' will work. When set to 'none' the element's formatting is ignored and the cells default to the spreadsheet's defaults.