If you trigger the 'Clear selection' button of the HTML5 Report Viewer parameter's area, there is no request for a report document with the updated parameter values and the viewer shows the previous report waiting for the user to select parameter values. This problem occurs with both Single and MultiValue parameters with AvailableValues that are non-nullable.

In the Standalone Designer and desktop viewers, in the same scenario, the preview displays a message indicating that the user needs to select valid parameter values.