The animation of the RadDock control is causes performance issues under IE8 and due to that the expanding/collapsing and the docking/undocking functionalities are not working as expected.

Disabling the animation resolves the issue: 
EnableAnimation="false"

When the content container of RadDock is configured to be a drag handle via the following code

dock.set_handle(dock.get_contentContainer());

a JavaScript error will be thrown if you call the 'clone' client-side function of the control

dock.clone()

When the browser or the page, on which a RadDock is placed, is configured with a culture that uses comma-separated values and you set the Width, Height, Top, Left properties with such a value, an exception will be thrown.

The rounded corners of RadDock controls that are using the Silk or Glow skin cannot be disabled.

When there is a RadDock with one or more disabled commands, you focus the dock and you use one of the default keyboard shortcuts for the disabled command(s), the keydown browser event will be disabled.

The default shortcuts are:

    ESC - Close command
    Ctrl + F11 - Toggle Expand / Collapse command
    Crtr + F12- Toggle Pin / UnPin command

As of Q1 2016 the elasticity of RadDock is not behaving properly due to  some fixed font styles like:
.RadDock .rdCommandButton
 {
     font-size: 16px;
 }

Possible workaround:
div.RadDock .rdCommandButton
 {
     font-size: 1.2em;
 }

When you place a resizable RadDock control (Resizable="true") in a RadDockZone without specified size and you close the dock, a JavaScript error is thrown.

When you dock a resizable RadDock (Resizable="true") in a RadDockZone, its drag handle is displaced in Chrome, which prevents you from resizing it when there are multiple docked docks.