[c-nsp] Strange ethernet frames on switch client ports

[Piltrafilla]

Hi people,

I am trying to completely clean up management frames on client ports
applying best common practices such as BPDU filtering

interface FastEthernetX/Y
 switchport access vlan NN
 switchport mode access
 no ip address
 no cdp enable
 spanning-tree portfast
 spanning-tree bpdufilter enable
 spanning-tree bpduguard enable
 spanning-tree guard root
!

This config removes 802.1d BPDUs, CDP frames, etc but on that port I
still see this management frames. I can't find which feature I must
disable in order to avoid them:

09:39:26.970184 0:f:90:fd:97:85 0:f:90:fd:97:85 9000 60:
                         0000 0100 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0000 0000 0000 0000
09:39:36.975274 0:f:90:fd:97:85 0:f:90:fd:97:85 9000 60:
                         0000 0100 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0000 0000 0000 0000
09:39:56.975158 0:f:90:fd:97:85 0:f:90:fd:97:85 9000 60:
                         0000 0100 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0000 0000 0000 0000

MAC address belongs to the switch as show mac-address-table says.

   All    000f.90fd.9785    STATIC      CPU

Anyone can give me some light on that? :)

Thank you in advance,