Awesome! I wonder if the problem was my fault with the vlan10-aka-vlan20 interface name... seems like the dashes messed it up. I was beginning to question that which is why I suggested you rename it in the last comment. Glad we did that!
Can you describe your goal here? Normally, you don't want to bridge different intefaces/VLANs as it defeats the purpose of VLANs... but maybe we're using slightly different terms.
The DSA syntax takes a while to wrap your head around... it will make sense if you do this enough, though.
DSA treats each physical port as an individual entity. A port may only be a member of a single interface or bridge. Therefore, where there is overlap, we create a single bridge that encompasses all relevant ports.
Then, we create bridge-VLANs -- this allows us to specify the VLAN-port-membership and the tagged/untagged status.
For each VLAN, we include only the relevant ports. The :t option specifies that a VLAN is tagged on that port. When we use :u* it means that the VLAN is untagged on that port (and PVID/default/native -- all untagged traffic on ingress/egress will be associated with that VLAN).
Meanwhile...
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Thanks! 