When I use the Offset tool I find that I must take care when I enter a specific ofset value if I want to use the Tab key to select "A chain of Walls or Lines". I get similar result when I use the Pick Lines option while drawing walls or lines.
The issue seems to be one of focus, Window's focus. That is what programmers refer to when a text box or similar control has the applications attention. When the offset value text box on the options bar has focus, Windows thinks the Tab key should be advancing to another control on the interface. In this case it advances to the Numerical radio button. I have to click in empty space in the drawing window to get the Tab key to do what I want. This put the focus back in the drawing window and Revit gets to define what the Tab key will do.
So watch out for this in your workflow.