what happens if an S-Series switch receives tagged a RSTP BPDU on a port?
Standard conforming spanning tree BPDUs are never tagged with a VLAN ID, but some devices add a .1Q tag with VLAN ID to otherwise standard BPDUs (e.g. Alcatel 1x1 mode, or Cisco IOS Rapid-PVST+ combined with tagging the native VLAN), and switches transparently forwarding BPDUs (e.g. because of disabled STP, as done by e.g. EXOS) will add a .1Q tag when a BPDU exits a port where the VLAN it is transported in is tagged.
I have observed the behavior of different switches in this situation, but not yet that of the S-Series:
EXOS 15.3 (IIRC) with enabled RSTP will accept the BPDU as if it did not have a tag. I have note checked this with later versions (later EXOS version incorporated quite a few STP changes and additions).
Quanta switches with Broadcom FASTPATH SWITCHING software will accept the BPDU as if it did not have a tag.
Arista switches will ignore the BPDU, but increment a counter and write a log message.
What does the S-Series with tagged BPDUs?
What do the A-Series, B-Series, C-Series, etc. with tagged BPDUs?