diff --git a/addons/web/static/src/js/action_manager.js b/addons/web/static/src/js/action_manager.js
index d1aa1fe3d06..de0f17691f3 100644
--- a/addons/web/static/src/js/action_manager.js
+++ b/addons/web/static/src/js/action_manager.js
@@ -203,8 +203,13 @@ var ActionManager = Widget.extend({
         this.inner_action = new_action;
         this.inner_widget = widget;
 
-        // Append the inner_widget and hide the old one
-        return $.when(this.inner_widget.appendTo(this.$el)).done(function () {
+        // render the inner_widget in a fragment, and append it to the
+        // document only when it's ready
+        var new_widget_fragment = document.createDocumentFragment();
+        return $.when(this.inner_widget.appendTo(new_widget_fragment)).done(function() {
+            self.$el.append(new_widget_fragment);
+            // Hide the old_widget as it will be removed from the DOM when it
+            // is destroyed
             if (old_widget) {
                 old_widget.$el.hide();
             }
diff --git a/addons/web_calendar/static/src/js/web_calendar.js b/addons/web_calendar/static/src/js/web_calendar.js
index 60597a32bfb..578826ccdeb 100644
--- a/addons/web_calendar/static/src/js/web_calendar.js
+++ b/addons/web_calendar/static/src/js/web_calendar.js
@@ -688,6 +688,12 @@ var CalendarView = View.extend({
         }
         this.event_source = {
             events: function(start, end, callback) {
+                // catch invalid dates (start/end dates not parseable yet)
+                // => ignore request
+                if (isNaN(start) || isNaN(end)) {
+                    return;
+                }
+
                 var current_event_source = self.event_source;
                 self.dataset.read_slice(_.keys(self.fields), {
                     offset: 0,