Unexpected STP Topology Changes

[telepath]

I have a 6509 acting as a distribution switch, one of the downliks is an old FO to a small site which every now and then has a small interruption that cause the whole network to recalculate the spanning tree, so I disabled stp on the access switch (Yeah I know cisco blasphemy) and set the link in the 6509 with bpdu-filter. Despite this, the 6509 keeps recalculating the stp (not very often really) and says the topology change came from the interface with bpdu filter and a switch (huawei 5720) with no stp.

Why does the 6509 recalculate STP when it is not supposed to process BPDU packets from that interface, which shouldn't be sending bpdu-tcn packets because the switch on the other side has no STP protocol on?


Thanks in advance.


Cisco 6509

switch# show spanning-tree detail | in ieee|from|occur|is exec
VLAN0001 is executing the ieee compatible Spanning Tree protocol
Number of topology changes 2126 last change occurred 02:59:48 ago from GigabitEthernet7/5
VLAN0505 is executing the ieee compatible Spanning Tree protocol
Number of topology changes 274 last change occurred 02:59:48 ago from GigabitEthernet7/5

......


interface GigabitEthernet7/5
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
spanning-tree bpdufilter enable


Switch Huawei:

<Switch >display stp topology-change
Info: The protocol is disabled.