In the ABAP/4 WORLD each stackable sequence of screens is a “call mode”, This is IMP because of the way u return from the given sequence .To terminate a call mode and return to a suspended chain set the “next screen” to 0 and leave to it:
LEAVE TO SCREEN 0 or (SET SCREEN 0 and LEAVE SCREEN) .When u return to the suspended chain execution resumes with the statement directly following the original CALL SCREEN statement.The original sequence of screens in a transaction (that is , without having stacked any additional call modes),you returned from the transaction altogether.