1, switch all ports can't be set to "yes" (it never becomes "yes", no error thrown"
2, all traffic is passed to firewall, despite ETH ports are set to slave mode

My installation:
-RB 493G
-all ETH ports part of switch1, switch2
-master of switch1 part of bridge
-traffic within switch1 ports is passed over for processing to firewall. Switch2 not tested.

/interface bridge
add admin-mac=00:0C:42:XX:XX:XX auto-mac=no l2mtu=1520 name=bridge1 protocol-mode=none
add name=guest-br
/interface bridge port
add bridge=guest-br interface=v-wlan1
add bridge=bridge1 interface="ether1 sw1 QN439"
add bridge=bridge1 interface=wlan1
add bridge=bridge1 interface="ether2 sw2"
/interface bridge settings
set allow-fast-path=yes use-ip-firewall=no use-ip-firewall-for-pppoe=no use-ip-firewall-for-vlan=no

/interface ethernet> print
Flags: X - disabled, R - running, S - slave
# NAME MTU MAC-ADDRESS ARP MASTER-PORT SWITCH
0 RS ether1 sw1 QN439 1500 00:0C:42:XX:XX:XX enabled none switch1
1 S ether2 sw2 1500 00:0C:42:XX:XX:XX enabled none switch2
2 S ether3 sw2 1500 00:0C:42:XX:XX:XX enabled ether2 sw2 switch2
3 S ether4 sw2 1500 00:0C:42:XX:XX:XX enabled ether2 sw2 switch2
4 R ether5-DSL 1500 00:0C:42:XX:XX:XX enabled none switch2
5 RS ether6 sw1 laptop 1500 00:0C:42:XX:XX:XX enabled ether1 sw1 QN439 switch1
6 RS ether7 sw1 DM8000 1500 00:0C:42:XX:XX:XX enabled ether1 sw1 QN439 switch1
7 S ether8 sw1 1500 00:0C:42:XX:XX:XX enabled ether1 sw1 QN439 switch1
8 S ether9 sw1 1500 00:0C:42:XX:XX:XX enabled ether1 sw1 QN439 switch1

NOTE: downgrade to 6.18 solved the issue.