<telerik:RadSlider ID="RadSlider_Ticks" runat="server" MinimumValue="0" MaximumValue="5"
                                        SmallChange="1" LargeChange="1" ItemType="tick" Height="40px" Width="400px" TrackPosition="TopLeft"
                                        AnimationDuration="400" ThumbsInteractionMode="Free" AutoPostBack="True"
                                         Skin="Metro"      RenderMode="Classic"  >
                                    </telerik:RadSlider>

When a RadSlider control is set with ItemType="Item" and has items that are not rendered (they are set with Visible="false"), the drag handle is positioned as if the invisible items are present in the slider.

When a RadSlider with Lightweight render mode and 100% width is vertically oriented, the text of its items has a fixed size that is not enough to fully display a larger text. 

When a RadSlider is in Lightweight render mode and it is configured to be vertically oriented, its decrease and increase handles are positioned outside of the container of the control. As a result they could appear in elements that are located above and below the slider.

Currently this can be avoided if you add margin to the slider:

    <style type="text/css">
        .rslVerticalSlider {
            margin: 2em 0;
        }
    </style>

    <telerik:RadSlider ID="RadSlider1" CssClass="rslVerticalSlider" runat="server"
             Orientation="Vertical" RenderMode="Lightweight">
    </telerik:RadSlider>

When the RadSlider control is in Lightweight render mode and its property TrackPosition is set to TopLeft, its elements are centered vertically or horizontally depending on the orientation of the control. It is easier to see this behavior when the slider has a bigger width in vertical orientation and bigger height in horizontal orientation.

The text of the slider items of RadSlider with ItemType="Item" and Orientation="Vertical" is aligned to the right.

RadSlider ticks are not positioned properly in IE11 with TrackPosition="TopLeft" and lightweight rendering.

When the width of the RadSlider is higher than 2100px, the Selected Region is looks broken.

If a horizontal RadSlider is set with ItemType=Tick or ItemType=Item, its decrease and increase handles are disabled and the MetroTouch/BlackMetroTouch skin is used, the ticks will not be positioned correctly. The effect depends on the value of the TrackPosition property:

   - If TrackPosition=TopLeft, all ticks will be misplaced.
   - If TrackPosition=BottomRight or TrackPosition=Center, the last tick will appear on a new line.