RS700 is sending BPDU packets only when in AP mode

I encountered an issue involving the Netgear RS300 operating in Access Point (AP) mode. I am also opening a support ticket for this behavior but thought I would post here in case anyone else has experienced a similar issue. 

Problem Description

When an RS300 running firmware 1.2.7.2 is connected to a Cisco switch port configured with BPDU Guard, the Cisco port immediately transitions to an err-disabled state.

Cisco switch log:

%SPANTREE-2-BLOCK_BPDUGUARD:Received BPDU on port Gi6/46 with BPDU Guard enabled. Disabling port. %PM-4-ERR_DISABLE:bpduguard error detected on Gi6/46, putting Gi6/46 in err-disable state

Wireshark Analysis

To isolate the problem, I disconnected the Cisco switch and connected only:

RS300 (AP Mode)      |      +--- Windows Laptop running Wireshark

No other networking devices were connected.

The RS300 LAN MAC address is:

28:94:01:0e:04:78

Using Wireshark with the filter:

stp

I observed the RS300 transmitting STP Configuration BPDUs approximately every two seconds.

Observed BPDU details:

Destination MAC: 01:80:C2:00:00:00
Protocol: Spanning Tree Protocol (STP)
BPDU Type: Configuration 
Root Identifier:28672 / 0 / 28:94:01:0e:04:78 
Bridge Identifier:28672 / 0 / 28:94:01:0e:04:78

The Root Identifier and Bridge Identifier match the RS300 LAN MAC address, indicating that the RS300 is originating the STP BPDUs and acting as the root bridge.

Firmware Comparison

I currently have two RS300 units available:

RS300 #1

Firmware:

1.0.1.90

Behavior:

AP Mode enabled - No STP/BPDU packets observed in Wireshark. Does not trigger Cisco BPDU Guard


RS300 #2

Firmware:

1.2.7.2

Behavior:

AP Mode enabled - Transmits STP Configuration BPDUs. Triggers Cisco BPDU Guard

This suggests a behavioral change or regression between firmware versions.

Downgrade Attempt

I attempted to downgrade the RS300 running firmware 1.2.7.2 to firmware 1.0.1.90.

The downgrade was rejected by the device and did not complete successfully.