When a RadPane with not configured fixed size is locked its size is not calculated properly (and the size of all its sibling free-sized panes).The issue can be reproduced with the following code in Firefox (both in horizontally or vertically oriented Splitter):

    <telerik:RadSplitter ID="TestSplitter" runat="server" Width="100%" Height="100%"
        Orientation="Horizontal">
        <telerik:RadPane ID="RadPane1" runat="server"
            Locked="true">
        </telerik:RadPane>
        <telerik:RadPane ID="RadPane2" runat="server">
        </telerik:RadPane>
        <telerik:RadPane ID="RadPane3" runat="server">
        </telerik:RadPane>
    </telerik:RadSplitter>

These overrides can be used as a temporary workaround:

        Telerik.Web.UI.SplitterPaneBase.prototype.get_height = function () {
            return this._height === "" ? 0 : parseInt(this._height);
        }
        Telerik.Web.UI.SplitterPaneBase.prototype.get_width = function () {
            return this._width === "" ? 0 : parseInt(this._width);
        }

The height of a  free-sized RadPane is not calculated properly on layout mode change in Android devices. The issue is reproducible in Firefox for Android.

A JavaScript error is thrown when a Splitbar is dragged in IE11 Edge mode and resolution 2560x1080. The issue is reproducible only when the ScriptManager's EnableScriptCombine property is set to False.

Temporary workaround: Set the RadScriptManager's EnableScriptCombine property to "True"

When a Splitter contains both RadPanes with size in percent and free-sized panes, the width of the fomer is calculated properly only after the initial loading and remains the same the the page is resized.

Steps to reproduce:
1.     <telerik:RadSplitter ID="RadSplitter1" runat="server" Width="100%">
            <telerik:RadPane ID="RadPane1" runat="server" Width="10%"></telerik:RadPane>
            <telerik:RadSplitBar ID="RadSplitbar1" runat="server" ></telerik:RadSplitBar>
            <telerik:RadPane ID="RadPane2" runat="server"></telerik:RadPane>
         </telerik:RadSplitter>

2. Resize the browser.

Result: the size of RadPane1 is not recalculated

Temporary workaround:
Set size in perncent to all RadPanes in the Splitter.

The tabs get hidden when a top oriented SlidingPane is docked inside a horizontal SlidingZone. The issue is reproducible when the resize mode of the parent Splitter is != AdjacentPane.

Steps to reproduce:
1. Run the following code:

        <div style="padding: 200px">
            <telerik:RadSplitter runat="server" ID="RadSplitter2" Orientation="Horizontal" ResizeMode="Proportional">
                <telerik:RadPane runat="Server" ID="radpane11" Height="20px" MaxWidth="980" Scrolling="None" BackColor="Green">
                    <telerik:RadSlidingZone ID="ListMetricsSlidingZone" runat="server" Height="25px" DockedPaneId="ListMetricsPane" SlideDirection="Top">
                        <telerik:RadSlidingPane ID="ListMetricsPane" Title="DEF" runat="server">
                            1111
                        </telerik:RadSlidingPane>
                        <telerik:RadSlidingPane ID="ListHistorySlidingPane1" Title="XYZ" Font-Size="X-Large" runat="server">
                            222
                        </telerik:RadSlidingPane>
                    </telerik:RadSlidingZone>
                </telerik:RadPane>
                <telerik:RadPane runat="Server" ID="radpane33" Scrolling="None">
                </telerik:RadPane>
            </telerik:RadSplitter>
        </div>

2. Undock and dock a sliding pane.

Expected: The tabs remains visible all the time (change the Splitters ResizeMode="AdjacentPane" for reference)

I have splitter tabs that show only images, no text--they are custom built so I get rotated text without worrying about browser compatibility.

I would like to use sprite images for the tabs rather than individual images.

The tabs of SlidingPanes are not rendered (sized) properly is the SlidingPane is containing a nested Splitter. The issue is not reproducible with 2014.2.724 version of the controls.

Reproduction code:
        <telerik:RadSplitter ID="RadSplitter2" runat="server" Skin="Metro">
            <telerik:RadPane ID="RadPane1" runat="server" Width="22px">
                <telerik:RadSlidingZone ID="RadSlidingZone1" runat="server" Width="22px">
                    <telerik:RadSlidingPane ID="RadSlidingPane2" Title="What If" runat="server">
                        <telerik:RadSplitter ID="WhatIfPaneSplitter" runat="server" Width="50px">
                            <telerik:RadPane ID="RadPane2" runat="server"></telerik:RadPane>
                            <telerik:RadPane ID="RadPane3" runat="server"></telerik:RadPane>
                        </telerik:RadSplitter>
                    </telerik:RadSlidingPane>
                </telerik:RadSlidingZone>
            </telerik:RadPane>
            <telerik:RadPane ID="RadPane4" runat="server"></telerik:RadPane>
        </telerik:RadSplitter>

I would like the ability to add attributes to the 'RadPane' iframe server side, example problem:

Suppose you have a page with an embedded you-tube video, the full screen option will be disabled as the iframe attribute 'allowfullscreen' is missing, this can be worked around using the following technique: 

http://www.telerik.com/forums/youtube-full-screen

However if the initial page has the youtube video the page needs to be loaded twice as chrome only picks it up on the second page load (as its been set in javascript).

If this is not possible, I would recommend you copy the approach used on radwindow (http://www.telerik.com/forums/youtube-video-in-popup-window-full-screen) e.g. 

    function setIframeAttr(sender, args) {
        var frame = sender.get_contentFrame();
        if (frame) {
            frame.setAttribute("allowfullscreen", "true");
        }
    }

With a client side event "OnClientBeforeShow" (OnClientShow does not work in internet explorer).

This isn't a priority but since there is a hack involved with reloading the page it may be worthwhile making it easier.

Chris

The text of the tabs inside a SlidingZone is not displayed properly when the SlidingZone is updated via AJAX. 

Steps to reproduce:
Run the following code and click a button inside a SlidingPane.

<telerik:RadSplitter ID="RadSplitter1" runat="server">
<telerik:RadPane ID="RadPane1" Scrolling="Both" Width="30px" runat="server">
<telerik:RadSlidingZone ID="RadSlidingZone1" runat="server" Width="30px">
<telerik:RadSlidingPane ID="RadSlidingPane1" runat="server" Title="Menu 1" Width="280px">
<telerik:RadButton runat="server" ID="btn1" AutoPostBack="true" Text="Update SlidingZone"></telerik:RadButton>
</telerik:RadSlidingPane>
<telerik:RadSlidingPane ID="RadSlidingPane2" runat="server" Title="Side Menu Two" Width="280px">
<telerik:RadButton runat="server" ID="btn2" AutoPostBack="true" Text="Update SlidingZone"></telerik:RadButton>
</telerik:RadSlidingPane>
</telerik:RadSlidingZone>
</telerik:RadPane>
<telerik:RadPane ID="AdditionalPane1" runat="server"></telerik:RadPane>
</telerik:RadSplitter>
<telerik:RadAjaxManager runat="server" ID="RadAjaxManager">
<AjaxSettings>
<telerik:AjaxSetting AjaxControlID="RadSlidingZone1">
<UpdatedControls>
<telerik:AjaxUpdatedControl ControlID="RadSplitter1" />
</UpdatedControls>
</telerik:AjaxSetting>
<telerik:AjaxSetting AjaxControlID="RadSlidingZone1">
<UpdatedControls>
<telerik:AjaxUpdatedControl ControlID="RadSplitter1" />
</UpdatedControls>
</telerik:AjaxSetting>
</AjaxSettings>
</telerik:RadAjaxManager>

Potential workaround is attached but it requires modification of the markup to add a class to the pane that holds the vertical sliding zone as well. If you do not need this fixed urgently, wait for an official fix.

RadSplitter is loaded with the gray background when configured with Default/Silks/Bootstrap skins in RenderMode="Classic".

The issue applies to RadFileExplorer and RadEditor file browser dialogs too which use RadSplitter inside.

The background is white in version 2017.1.118.40 and earlier.

Workaround:
Switch to RenderMode="lightweight"

or 

RadSplitter: Apply the BackColor property to RadSplitter or its RadPane items.
RadFileExplorer: 
ASPX:
<telerik:RadFileExplorer ID="RadFileExplorer1" runat="server" RenderMode="Classic">
    <Configuration ViewPaths="~/"  />
</telerik:RadFileExplorer>
Codebehind:
using Telerik.Web.UI;

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        (RadFileExplorer1.Splitter.GetPanes()[0] as RadPane).BackColor = System.Drawing.Color.White;
        (RadFileExplorer1.Splitter.GetPanes()[1] as RadPane).BackColor = System.Drawing.Color.White;
    }
}

Endless Loading screen is shown over RadPane when the set_showContentDuringLoad(false) method before changing the contentUrl of a RadPane (which is already showing another external page).