This issue was reported by one of corporate user when he downloaded a report in siebel analytics in excel format. The issue is in the report he could see few values in date format but when he downloaded, all the values in date column become null.
This issue is only reproduced excel download.
On investigation, i found that the one of the column of the report was having values starting with'-' sign and whenever we have this value in the report, we were facing this issue. In excel, any value with '-' is treated for reference value.
So analytics could not identify the reference when it tried write the report in excel format.
it's resolved by truncating the '-' sign or users were asked to correct it while entering the decription.
let me know if you need more clarification.