A good friend of mine asked me if the issues that I am facing with plcd are caused by poor design of the Insteon protocol. Here is my response to him.
The insteon protocol is a PITA for what I am doing, but, you have to remember it is designed to work without a computer controller. Take the "groups" for example. A controller can trigger each responder in its group withits own on level and ramp rate (for 400 or so devices), and each group reacts simultaneously. With powerline signalling you simply don't have the bandwidth to signal each device separately with levels and ramp rates, all you can do is broadcast a message asking the devices in the group to return to a previous level. Bear in mind, each responder can have many controlling devices, and you have to set this up without a computer too.
You can actually see this phenomenon with the outside lights. plcd doesn't build groups for macros, it could, and possibly it should, but I have so far elected not to because of the ability to delay macro commands. When you use a switch to turn the outside lights on it is done through direct grouping between the two light circuits and they go on simultaneously. In the case of plcd turning them on, there is a slight (0.5 seconds or so) delay between turning one on vs the other as each one is signalled separately.
So yes there are limitations, and yes, they are causing some hoop jumping, but to blame them on poor design is not as simple a statement.