Coarray SYNC ALL issue

The following code exhibits a different behavior depending on whether line 3 or 4 is commented out. It seems that the SYNC ALL behavior varies depending on which image 'finishes first'.

PROGRAM MAIN
IMPLICIT NONE
IF (THIS_IMAGE()==1) THEN   ! This works.
!IF (THIS_IMAGE()==2) THEN   ! Any image number > 1 causes the code to hang at the SYNC ALL below.
    CALL SLEEP(1)
    WRITE(*,*) 'Image ',THIS_IMAGE(),' is done!'
    GO TO 100
END IF
SYNC ALL
WRITE(*,*) 'Image ',THIS_IMAGE(),' is done!'
100 CONTINUE
END PROGRAM MAIN