I'm afraid this isn't working for me either. Build 460. I'm working with the AIR SDK in Flex 4 beta 1. Tab causes a new-line to appear (not a tab) in the TextFlow and then the focusManager kicks in, tabbing to the next Flex control.
The default behavior when there are no tab stops before the end of the line is to create a new line exactly as you describe. Please verify that you've specified tab stops.
This is even simpler than the above.
will create tabs at 100 and 200 pixels.