When developing a Telerik report template with the intention of exporting to Excel, I observed the % sign was not displaying for positive numbers in the exported Excel file. The format we were using was {0:N2}%. The results displayed on the HTML report viewer and the Word export document was correct:

However in the excel file result, the cells were formatted without the % for positive numbers, and with the % for negative numbers.

Upon further inspection, I noticed the excel cell formatting was translated as:

This format would not generate the % symbol for a positive number as the trailing % is missing before the semi-colon.

We are fixing this by using the below Format specification directly in the Report Designer:

{0:#,##0.00"%";-#,##0.00"%"}

which is directly retained in the excel custom format:

While I understand that N, C etc. C# number formats are supported according to the design considerations and this bug is also technically resolved by using UseExtendedFormatting (setting this to false translates {0:N2} to #,##0.00"%"), this seems like an unexpected result of translating the format codes that does not match the standard behavior of {0:N2}%. Reporting this behavior for review.