Workaround:


        public class CustomPageView : RadPageView
        {
            public override string ThemeClassName  
            { 
                get 
                { 
                    return typeof(RadPageView).FullName;  
                }
            }

            protected override RadPageViewElement CreateUI()
            {
                if (this.ViewMode == PageViewMode.NavigationView)
                {
                    return new CustomRadPageViewNavigationViewElement();
                }
                return base.CreateUI();
            }
        }

        public class CustomRadPageViewNavigationViewElement : RadPageViewNavigationViewElement
        {
            protected override Type ThemeEffectiveType     
            { 
                get    
                { 
                    return typeof(RadPageViewNavigationViewElement);     
                }
            }

            public override void Expand()
            {
                if (!this.IsCollapsed)
                {
                    return;
                }

                FieldInfo pi = typeof(RadPageViewNavigationViewElement).GetField("isCollapsed", BindingFlags.NonPublic | BindingFlags.Instance);
                pi.SetValue(this, false); 
                this.ItemContainer.Visibility = ElementVisibility.Visible;

                NavigationViewDisplayModes mode = this.GetEffectiveDisplayMode(this.Size.Width);

                if (mode == NavigationViewDisplayModes.Expanded)
                {
                    
                    this.ItemContainer.MinSize = new Size(this.ExpandedPaneWidth, 0);
                }
                else
                {
                    this.PopupStack.Children.Insert(0, this.HamburgerButton);

                    if (!this.PopupStack.Children.Contains(this.ItemContainer))
                    {
                        this.PopupStack.Children.Add(this.ItemContainer);
                    }

                    this.HamburgerButton.Alignment = this.RightToLeft ? ContentAlignment.TopRight : ContentAlignment.TopLeft;
                    this.HamburgerButton.StretchHorizontally = true;
                    this.ItemContainer.ItemLayout.SetValue(RadPageViewStripElement.StripAlignmentProperty, StripViewAlignment.Right);
                    this.ItemContainer.ResetValue(RadElement.MinSizeProperty, ValueResetFlags.Animation);
                    this.ItemContainer.MinSize = new Size(this.ExpandedPaneWidth, 0);
                    this.ItemContainer.MaxSize = Size.Empty;

                    foreach (RadPageViewItem item in this.Items)
                    {
                        item.DrawText = true;
                    }

                    if (this.Popup.ElementTree.RootElement.ElementState != ElementState.Loaded)
                    {
                        Size size = new Size(this.ExpandedPaneWidth, (int)this.DesiredSize.Height);
                        this.Popup.LoadElementTree(size);
                    }

                    ApplyThemeToPopup(this.ElementTree, this.Popup);

                    this.Popup.Size = new Size(this.ExpandedPaneWidth, (int)this.DesiredSize.Height);
                    this.Popup.DropDownAnimationDirection = this.RightToLeft ? RadDirection.Left : RadDirection.Right;
                    this.Popup.HorizontalPopupAlignment = this.RightToLeft ? HorizontalPopupAlignment.RightToRight : HorizontalPopupAlignment.LeftToLeft;
                    this.Popup.VerticalPopupAlignment = VerticalPopupAlignment.TopToBottom;
                    this.Popup.RootElement.BackColor = this.BackColor;

                    this.Popup.Show(this.PointToScreen(this.RightToLeft ? new Point(this.Bounds.Right, this.Bounds.Top) : new Point(this.Bounds.Left, this.Bounds.Top)));
                }
            }

            public override void Collapse()
            {
                if (this.IsCollapsed)
                {
                    return;
                }
                FieldInfo pi = typeof(RadPageViewNavigationViewElement).GetField("isCollapsed", BindingFlags.NonPublic | BindingFlags.Instance);
                pi.SetValue(this, true); 

                foreach (RadPageViewItem item in this.Items)
                {
                    item.DrawText = false;
                }

                NavigationViewDisplayModes mode = this.GetEffectiveDisplayMode(this.Size.Width);             

                if (mode == NavigationViewDisplayModes.Expanded)
                {
                    this.ItemContainer.MinSize = new Size(this.CollapsedPaneWidth, 0);
                }
                else
                {
                    FieldInfo fi = typeof(RadPageViewNavigationViewElement).GetField("programmaticallyClosingPopup", BindingFlags.NonPublic | BindingFlags.Instance);
                    fi.SetValue(this, true); 
                    this.Popup.ClosePopup(RadPopupCloseReason.Mouse);
                    this.HamburgerButton.StretchHorizontally = false;
                    fi = typeof(RadPageViewNavigationViewElement).GetField("programmaticallyClosingPopup", BindingFlags.NonPublic | BindingFlags.Instance);
                    fi.SetValue(this, false); 

                    if (mode == NavigationViewDisplayModes.Compact)
                    {
                        this.ItemContainer.MinSize = new Size(this.CollapsedPaneWidth, 0);
                        this.ItemContainer.MaxSize = new Size(this.CollapsedPaneWidth, 0);

                        if (!this.Children.Contains(this.ItemContainer))
                        {
                            this.Popup.RootElement.ResetValue(RadItem.BackColorProperty, ValueResetFlags.Local);
                            this.Children.Insert(0, this.ItemContainer);
                        }
                    }

                    if (!this.Children.Contains(this.HamburgerButton))
                    {
                        this.HamburgerButton.ResetValue(AlignmentProperty, ValueResetFlags.Local);
                        this.Children.Add(this.HamburgerButton);
                    }
                }
            }
        }