shift+tab behavior in tool bars

According to the WAI-ARIA practise - Tab moves focus to the first enabled
button in a toolbar.

I am taking the below link as an example:

http://www.oaa-accessibility.org/examplep/toolbar1/

1) Tab to first button in Text formatting controls under Text Sample 1

2) Press right arrow key to reach the second button

3) Press Tab, it will reach the first button in the Paragraph formatting
control.

4) Press shift + tab - the focus will move to the second button in Text
formatting controls.

Is the 4th step expected behavior? Or should the first button receive focus
by default on doing reverse tab?
The design pattern for toolbar does not provide advice on reverse tab order

-- 
with regards

Steve Faulkner

<http://www.paciellogroup.com/resources/wat-ie-about.html>