Hi,
I did get an confirmation from JTAC that there is an issue with certain IOS releases. But from what I understood, there was no fix available and the root cause was not identified.
We rebuilt the topology and removed the Cisco < > Juniper L2 connection.
You can also add a FW filter and filter out BPDUs on ports that you have control over. But we have seen unwanted BPDUs anyway on those. Quite wierd.
//Robert