For anyone else wth a similar potential problem, this was a good thread with lots of details:
At one point the poster had one of my problems, which is that even trying to 'arm' through the web UI didn't do anything. Unfortunately, he says an update last year helped him, though I am already up-to-date.
With the discovery I'm not even able to arm intrusion within the web UI (though disarming smoke/CO monitoring in the web UI seems to work), I'm now thinking my problem is bigger than just not being able to elect buttons on power plugs to be responsible for arming.
