Ath9k doesn't respect setting country and stuck at max TX 18 dBm

Device: TP-Link WR741ND v4
OS: LEDE 17.01.2, also tried compile trunk with ATH_USER_REGD=y

I tried set country via

iw reg set TW

and via /etc/config/wireless and reboot router - no matter, ath9k ignore this settings.

root@lede:~# iw reg get
global
country TW: DFS-FCC
        (2400 - 2483 @ 40), (N/A, 30), (N/A)
        (5150 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
        (5250 - 5350 @ 80), (N/A, 23), (0 ms), DFS, AUTO-BW
        (5470 - 5725 @ 160), (N/A, 23), (0 ms), DFS
        (5725 - 5850 @ 80), (N/A, 30), (N/A)

phy#0
country US: DFS-FCC
        (2402 - 2472 @ 40), (N/A, 30), (N/A)
        (5170 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
        (5250 - 5330 @ 80), (N/A, 23), (0 ms), DFS, AUTO-BW
        (5490 - 5730 @ 160), (N/A, 23), (0 ms), DFS
        (5735 - 5835 @ 80), (N/A, 30), (N/A)
        (57240 - 63720 @ 2160), (N/A, 40), (N/A)

As you can see, phy#0 always “country US” and max TX 18 dBm

root@lede:~# iw dev
phy#0
        Interface wlan0
                ifindex 8
                wdev 0x3
                addr 10:fe:ed:xx:xx:xx
                ssid LEDE
                type AP
                channel 11 (2462 MHz), width: 20 MHz, center1: 2462 MHz
                txpower 18.00 dBm

Can this be related to EEPROM hard-coded values? How I can check it?

https://bugs.lede-project.org/index.php?do=details&task_id=861