Temporary CSS-based workaround:
1. In the settings page for the Reports Module instances you wish to hide the headers for, append "HideHeaders" to the "CSS Class" setting for the Grid Visualizer (you may have as many space-separated CSS classes here as you want, order does not matter).
2. Open the file ~/Portals/[PortalID]/portal.css for the portal(s) you wish to hide the headers for, and add the BOLDED CSS (non-bolded lines should already exist and are shown for context)
/* ================================
CSS STYLES FOR DotNetNuke
================================
*/
/* TEMPORARY WORKAROUND FOR Reports Module BUG */
table.HideHeaders tr.DNN_Reports_Grid_Header {
display:none;
}
/* PAGE BACKGROUND */
/* background color for the header at the top of the page */
.HeadBg {
}
This can also be done using the Stylesheet editor on the Admin > Site Settings menu.
Save changes, and the headers should disappear. This will only affect those modules with the CSS Class attribute set to "HideHeaders". If this name conflicts with another CSS Class in your portal, change it in both the Module Settings and CSS File. Since this workaround does not add any additional code, and only affects Reports Modules with a certain CSS Class, it should be safe for use in production, but ensure you back up your CSS files BEFORE changing them, just in case.
NOTE: The Headers will still be present in the HTML file.