The size of a dock is increased a bit each time it is dropped and the  EnableAnimation="True".

Video: https://www.screencast.com/t/LoUJbAb8c

Workaround:
Set EnableAnimation="False"

Steps to reproduce:
1. Run the following code.
2. Swipe the first and second dock several times (Test 1 and Test 2)

                <telerik:RadDockZone ID="Zone1" runat="server" Height="500px" Orientation="Horizontal" Width="400px">
                    <telerik:RadDock RenderMode="Lightweight" runat="server" Height="110px" Width="140px" ID="RadDock1" Title="RadDock A" DefaultCommands="None" DockMode="Docked"
                        EnableAnimation="True" EnableRoundedCorners="True" Skin="Silk">
                        <ContentTemplate>
                            <div style="background-color: blue; width: 110px; color: white">
                                Test 1
                            </div>
                        </ContentTemplate>
                    </telerik:RadDock>
                    <telerik:RadDock RenderMode="Lightweight" runat="server" Height="110px" Width="140px" ID="RadDock2" Title="RadDock B"
                        DefaultCommands="None" DockMode="Docked" EnableAnimation="True" EnableRoundedCorners="True" Skin="Web20">
                        <ContentTemplate>
                            <div style="background-color: red; width: 110px; color: white">
                                Test 2
                            </div>
                        </ContentTemplate>
                    </telerik:RadDock>
                    <telerik:RadDock RenderMode="Lightweight" runat="server" Height="110px" Width="140px" ID="RadDock3"
                        Title="RadDock C" DefaultCommands="None" DockMode="Docked" EnableAnimation="True" EnableRoundedCorners="True" Skin="Web20">
                        <ContentTemplate>
                            <div style="background-color: green; width: 110px; color: white">
                                Original
                            </div>
                        </ContentTemplate>
                    </telerik:RadDock>
                </telerik:RadDockZone>


Result: The width of the first two docks is different than the one which has not been dragged (Original)

Expected: The width of all docks remains the same.