WIFI devices arent using 2.4Ghz 40MHZ band?

[greyfreak19]

i have set 40Mhz in the router devices still dont go above 72Mbits in the router status and the pc the settings page shows that 40Mhz is active whats wrong? i triend 1.8.1 (on currently) 1.9.0,1.9.X ispy build (where i noticed the problem)

http://imgur.com/Bv57Ofq

Router: TP-Link TL WR-841N V9 (4mb flash rotuer)

40MHz worked just fine before

EDIT:
i fixed this by manually settings he transmit power from max to 21 as i know 21 is the max my unit will do for some reason settings 30manually or settings max in the transmit power makes 40Mhz not work anymore i only get 20Mhz speeds now it seems to be fine

[Lantis]

You will probably find that it truly is using 20MHz if there are lots of wireless networks around you. This is s regulatory requirement. "Good neighbour" clause.