I have reported this problem on kernel.org and it is assigned as a bug (bugzilla.kernel.org id=75541)
It was recommended to replace the iwconfig commands with iw commands
Changing to the iw commands had no effect.
Further testing showed that the 7260-8 firmware does operate successfully if channel 1 is selected, but it locks if any other channel is selected
Since the card provides functionality on all channels if 7260-7 firmware is used, the problem is not the card, it is the firmware.
There is no support from the sites referenced, I used both of them to find the kernel version recommendation and the version of firmware recommended.
I was hoping the latest version of firmware would solve the core problem which is the periodic total dropout of wifi reception (we use the card in monitor mode in our product). But the latest firmware is obviously not a solution, and I don't know if it solves the problem we are trying to fix.
But I see that many people are having this problem on a variety of platforms, so it seems the reliability of this card is below what we need in our product and we need to look at a different card.
The issue with the 7260-8 firmware locking the kernel was an issue in the iwlwifi driver. A patch has been prepared (see bugzilla.kernel.org id=75541)
I can proceed with further testing now to see if the 7260-8 firmware resolves the problem with the wifi reception shutting down periodically when in monitor mode.
I purchased an Intel 7260HMW (802.11ac) card to replace the original 802.11n card in my Intel NUC DN2820FYKH. The DN2820 was recently upgraded to OpenELEC 4.0.0 which has the Linux 3.14.2 kernel. The card could see both the 2.4GHz and 5.0GHz bands from my ASUS RT-AC68U 802.11ac router. When connecting to either band, if I stream video over the network, the stream starts and stops a few times in less than a minute and then the 7260HMW drops the connection to the router. I re-installed the 802.11n card and the network worked without problems. OpenELEC 4.0.0 has the 7260-8 firmware. I was not successful in adding the 7260-9 firmware file to the /lib/firmware directory. I hope the patch mentioned in the previous post can fix the problems I'm seeing with the 7260HMW.