Tabulation beetween widgets.

Under PhAb, I’ve defined a PtPane with several fields inside it (PtList, PtCombo, PtText, …) on which Tabulations has the following behaviour:
Tab works from the first to the last widget inside the PtPane;
Shift Tab doesn’t work (in order to go to previous Widget …);
What is the way to loop from the last to the first (if Tab is used …) or from the first to the last (if Shift Tab is used …) ?

Thx for your help !