The router seems to accept and save/apply my change to 40 MHz. If I logout and login again the router shows 40 MHz in the menu but when I test with a wifi analyzer it reports that the router still uses 20 MHz. In the log I can't find any report related to the change. I have done a few factory resets but it doesn't help.
In firmware 00.01.06 I had the same problem but after a lot of tries the router suddenly changed to 40 MHz. I don't know why as I used the same procedure all the time.
With fw 00.02.00 I haven't done so many tries. The router stays in 20 MHz mode whatever I do!