When modifying the XSL Reporting you may want to make sure you are using the correct folder. The Report files are stored in this location, replacing the year with your product.
As long as you are running the reports from within Civil 3D you should be good to go. If you are using the LandXML reporting then you might end up with some problems. The Reporting tool typically utilizes the most recent version of Civil 3D (or maybe the last installed version, I don’t really know). So make sure the reports are utilizing the correct version you have modified. You can check by looking at the file location on the Forms Tab of the LandXML Reporting Tool:I guess I should really start using the Last Modified By: field.