SXT w/ bridge and simple queue stops passing traffic

Hi,

our MikroTik SXTs stop passing PPPoE traffic/passes traffic really slow (e.g. with 50 kbps) with configured bridge and simple queue on ether1 interface after some random time. Only PPPoE traffic is allowed to pass the bridge. Problem exists on RouterOS v6.7 and earlier.

After setting use-ip-firewall=no in bridge settings and disabling simple queue traffic gets passed over the bridge with full speed again - but of course, without the requried bandwidth limitation.

SXT 5HPnD in station-wds mode, ether1 and wlan1 bridged by bridge1, simple queue on ether1:

/interface wireless> print 
Flags: X - disabled, R - running 
 0  R name="wlan1" mtu=1500 mac-address=D4:CA:6D:XX:XX:XX arp=enabled
      interface-type=Atheros AR92xx mode=station-wds ssid="xxxxxxx" frequency=5470 
      band=5ghz-a/n channel-width=20mhz scan-list=5470-5720 wireless-protocol=nv2
      wds-mode=disabled wds-default-bridge=none wds-ignore-ssid=no 
      bridge-mode=enabled default-authentication=yes default-forwarding=yes
      default-ap-tx-limit=0 default-client-tx-limit=0 hide-ssid=no 
      security-profile=default compression=no

/interface bridge settings> print 
            use-ip-firewall: yes
   use-ip-firewall-for-vlan: no
  use-ip-firewall-for-pppoe: yes
            allow-fast-path: yes

/interface bridge filter> print 
Flags: X - disabled, I - invalid, D - dynamic 
 0   chain=forward action=accept in-interface=ether1 in-bridge=bridge1
     out-interface=wlan1 mac-protocol=pppoe 

 1   chain=forward action=accept in-interface=ether1 in-bridge=bridge1
     out-interface=wlan1 mac-protocol=pppoe-discovery 

 2   chain=forward action=drop in-interface=ether1 in-bridge=bridge1
     out-interface=wlan1 

/queue simple> print 
Flags: X - disabled, I - invalid, D - dynamic 
 0    name="queue1" target=ether1 parent=none packet-marks="" priority=8/8
      queue=default-small/default-small limit-at=0/0 
      max-limit=512k/12M burst-limit=0/0 burst-threshold=0/0 burst-time=0s/0s

Any ideas why the queue gets stalled after some indeterminable/random time? Thank you!

Regards,
Robert