Then the HTML5 ReportViewer is set to pageMode SINGLE_PAGE and an update triggeres the Viewer to retrieve the document, the new document is never displayed. 

Status messages appear as usual, "Loading report", "0 pages loaded so far" and "Done. Total 1 pages loaded." but the gray overlay of the Viewer is never removed and the report is not updated. Parameters and toolbar-menu can still be interacted with and trigger new updates, but will not cause the viewer to show the report correctly. Refresh required