If the HTML5 Report Viewer gets hidden on renderingBegin(e, args) event and shown on renderingEnd(e, args) event, its toolbar is shown, but the contents are still invisible.
Code snippet that demonstrates the issue:
$("#reportViewer1")
.telerik_ReportViewer({
... initialization script goes here
renderingBegin: function (e, args) {
$("#reportViewer1").hide();
},
renderingEnd: function (e, args) {
$("#reportViewer1").show();
}
});