ProCurve 1800-24G Switches causing Spanning Tree problems on Cisco Router

[Azannah]

I have 3 ProCurve 1800-24G switches. Two of the switches are connected to the third using two aggregated links. The third switch is also connected to an HP ProLiant server using a teamed NIC (2 ports). A Cisco 871 router (which I have no control over) is connected to the first switch.

Occasionally, a change in the configuration of one of the switches (first, second, or third) will cause what looks like a broadcast storm. When this happens, the RSTP on the Cisco router shuts down the port connected to the first switch.

The Cisco remains in blocking mode until someone walks in to the network closet, unplugs the port in question for 30 seconds, and plugs it back in.

This happened today when I mirrored port 5 to port 7 on the third switch...

Any ideas why this happens? Can anyone think of a way to keep it from happening?

[Azannah]

I found a FAQ (http://www.hp.com/rnd/support/faqs/1800.htm) which states that the 1800-24G doesn't even pass BPDUs, so I don't know how the Cisco 871 would detect itself... Maybe this isn't a STP problem at all, but something else?

Frustrating.