Doubt on 802.1w (max age)

Hi,

Setup:
     6 manageable switches are connected in linear fashion with root brdige
at top . In the root bridge ,max-age ,hellotime and forward-delay is
configured  as 6 ,1 and 4 .


Issue :
    In the sixth bridge ,learned value of max-age,hello time and forward
delay is found as 6 ,1 and 4.But the role of the port connected to
switch 6 alone is switching between F/R (Root) and F/D (Designated )



    We r using the source forge rstp source code for all 6 switches
    From 802.1w standard,I calculated the  rcvdinfowhile timer value for
the port connected to sixth switch as 1 (Calculation done from
updtRcvdInfoWhile()) .When port of switch 6 recieves BPDU  for every
hello time (1 sec) port role switches to F/R and on expiry of
rcvdInfoWhile timer expiry ( 1 sec ) port role switches to F/D .

   What do you think about it ?