Hi Ivan,
In addition to this issue (which seems to depend on whether the elements to shift-tab out to are in a containing div), I've found what I think is another problem.
If resizable is set to false, then the focus using shift-tab always *stops* at the second toolbar button. This is seen on the Telerik-supplied demo here at dojo: in the "Non-resizable Toolbar" toolbar, tab to "Button 4", then attempt to shift-tab to "Button 1". The focus stops at "Button 2" and won't go any further back.