M4300-24X problem with "Spanning Tree Topology Change" filling up the log

Hi

I have a problem that the log on MX4300 are filling upp with (1 message/2s):

"TRAPMGR[dot1s_task]: traputil.c(795) 1181606 %% Spanning Tree Topology Change Received: VLAN ID: 1 lag 1"

I have a MX4300-24X connected to a Cisco 3750G switch (trunk port for multiple VLANS) with a LAG on the Netgear side and a port channel on the Cisco side

Both switches have spanning tree set to PVST

Everything seems to work as it should (the LAG/port channel is up with the all the connected ports)

Spanning tree is not indicating any blocks

I have set the Cisco switch priority to 8192 for the spanning tree

If I look att the spanning tree in MX4300 for VLAN 1 I get this: (00:12:00:DD:CD:00 is my Cisco switch)

Spanning-tree enabled protocol pvst

VLAN 1
RootID Priority 8193
Address 00:12:00:DD:CD:00
Cost 5000
Port 1(lag 1 )
Hello Time 2 Sec Max Age 20 sec Forward Delay 15 sec
BridgeID Priority 32769 (priority 32768 sys-id-ext 1)
Address 28:80:88:71:23:84
Hello Time 2 Sec Max Age 20 sec Forward Delay 15 sec
Aging Time 3000 sec

Interface State Prio.Nbr Cost Status Role
--------- --------- --------- --------- ------------- -----------
lag 1 Enabled 128.770 5000 Forwarding Root

Everything seems OK, so I don´t understand why Netgear are logging topology change