BPDU Filtering

Hello,

Switch Model - PowerConnect 5424

SW version - 2.0.0.46

I have a problem with BPDU Filtering (Spanning-Tree)

this is my topology (attached picture), both switches working fine with STP - MST

(CISCO Switch is the - root bridge for instance 1 + 2).

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My problem appear when i connect new switch to Dell PowerConnect 5424 that is working with PVST, but the connection port configured with STP DISABLE + global configuration (spanning-tree bpdu filtering).

In this situation the Dell Switch become the root bridge for instance 1 + 2.

What can i do to block bpdu message (PVST) from the new Switch that connect to dell and working with PVST. (Attached example),

Thanks,