I also experience similar issue. My router is 1043nd v1.8 + OpenWRT (ATTITUDE ADJUSTMENT (12.09-rc1, r34185)).
My config is as following:
I tried different wmm and htmode but problem still persists. Once it is reproduced i will post log and dmesg.
root@OpenWrt:~# uname -a
Linux OpenWrt 3.3.8 #1 Sun Nov 18 04:31:55 UTC 2012 mips GNU/Linux
root@OpenWrt:~# lsmod
Module Size Used by Tainted: G
option 14992 0
sg 18864 0
usb_wwan 6560 1 option
usbserial 23792 2 option,usb_wwan
ath79_wdt 2240 1
ledtrig_usbdev 2032 0
ledtrig_netdev 3184 0
nf_nat_irc 784 0
nf_conntrack_irc 2464 1 nf_nat_irc
nf_nat_ftp 976 0
nf_conntrack_ftp 4416 1 nf_nat_ftp
xt_HL 1200 0
xt_hl 720 0
xt_ecn 1168 0
ipt_ECN 1264 0
xt_CLASSIFY 496 0
xt_time 1456 0
xt_tcpmss 912 0
xt_statistic 688 0
xt_mark 592 0
xt_length 608 0
xt_DSCP 1360 0
xt_dscp 912 0
ipt_MASQUERADE 976 1
iptable_nat 2544 1
nf_nat 10256 4 nf_nat_irc,nf_nat_ftp,ipt_MASQUERADE,iptable_nat
xt_recent 5696 0
xt_helper 784 0
xt_connmark 960 0
xt_connbytes 1424 0
pppoe 7488 0
xt_conntrack 2048 3
xt_CT 1216 0
xt_NOTRACK 448 0
iptable_raw 560 1
xt_state 608 0
nf_conntrack_ipv4 4384 6 iptable_nat,nf_nat
nf_defrag_ipv4 656 1 nf_conntrack_ipv4
nf_conntrack 38208 15 nf_nat_irc,nf_conntrack_irc,nf_nat_ftp,nf_conntrack_ftp,ipt_MASQUERADE,iptable_nat,nf_nat,xt_helper,xt_connmark,xt_connbytes,xt_conntrack,xt_CT,xt_NOTRACK,xt_state,nf_conntrack_ipv4
pppox 1152 1 pppoe
ipt_REJECT 1808 2
xt_TCPMSS 2560 1
ipt_LOG 6160 0
xt_comment 400 0
xt_multiport 1104 0
xt_mac 528 0
xt_limit 944 1
iptable_mangle 832 1
iptable_filter 592 1
ip_tables 8864 4 iptable_nat,iptable_raw,iptable_mangle,iptable_filter
xt_tcpudp 1632 5
x_tables 9984 34 xt_HL,xt_hl,xt_ecn,ipt_ECN,xt_CLASSIFY,xt_time,xt_tcpmss,xt_statistic,xt_mark,xt_length,xt_DSCP,xt_dscp,ipt_MASQUERADE,iptable_nat,xt_recent,xt_helper,xt_connmark,xt_connbytes,xt_conntrack,xt_CT,xt_NOTRACK,iptable_raw,xt_state,ipt_REJECT,xt_TCPMSS,ipt_LOG,xt_comment,xt_multiport,xt_mac,xt_limit,iptable_mangle,iptable_filter,ip_tables,xt_tcpudp
ppp_async 5952 0
ppp_generic 18848 3 pppoe,pppox,ppp_async
slhc 4368 1 ppp_generic
ath9k 85472 0
ath9k_common 1152 1 ath9k
ath9k_hw 316864 2 ath9k,ath9k_common
ath 14320 3 ath9k,ath9k_common,ath9k_hw
mac80211 252240 1 ath9k
crc_ccitt 944 1 ppp_async
cfg80211 153696 3 ath9k,ath,mac80211
compat 5776 5 ath9k,ath9k_common,ath9k_hw,mac80211,cfg80211
arc4 768 2
aes_generic 29808 5
usb_storage 33152 2
ohci_hcd 16160 0
ehci_hcd 33632 0
sd_mod 22240 3
ext4 237824 1
jbd2 37248 1 ext4
mbcache 3504 1 ext4
usbcore 99200 8 option,usb_wwan,usbserial,ledtrig_usbdev,usb_storage,ohci_hcd,ehci_hcd
usb_common 480 1 usbcore
scsi_mod 69904 3 sg,usb_storage,sd_mod
nls_base 4640 1 usbcore
crc16 944 1 ext4
crypto_algapi 9200 2 arc4,aes_generic
ledtrig_timer 1072 0
ledtrig_default_on 416 0
leds_gpio 1552 0
gpio_button_hotplug 3184 0