I've been running an ISY 99i Pro for some time now but have only been controlling X-10 devices.
I finally broke down and purchased some Insteon devices (SwitchLinc Dimmer and SwitchLinc Relays). I had some initial trouble adding a couple of devices. The problem, I believe, was due to the devices being on a different phase than the PLM. When I was finally successful in adding them, they weren't reporting status.
What I eventually found was that the PLM had multiple links to the devices. After I cleaned up the PLM links and re-linked the devices, they worked fine.
Don