Hi,
1) Could you give us some more details about this problem? When you say "Excel Exporter", do you mean exporting to Excel using the "JRXlsExporter" class, or the "JExcelApiExporter" one?
2) When using POI (ie JRXlsExporter) there are a set of builtin data format patterns (see http://jakarta.apache.org/poi/apidocs/org/apache/poi/hssf/usermodel/HSSFDataFormat.html), and a set of recognized format symbols. Unfortunately, the timezone \'z\' or \'Z\' characters are not included, and so are the \'E\', \'w\' and \'W\' too. Excel does not recognize them as part of date formatting. That explains them being written "as it is".
We introduced a new exporter parameter (FORMAT_PATTERNS_MAP) to allow translating the
text field patterns to XLS exporter specific cell format patterns. This is a map containing the classic java format pattern as key, and the corresponding proprietary format pattern as value, and you can see an example after downloading compiling and executing the "jasper" sample (http://scm.jasperforge.org/svn/repos/jasperreports). The corresponding pattern you choose may not look 100% like the java pattern, you have to decide the better way to keep the most part of information in the new data representation.
Regards,
sanda