LDCad 1.7 Alpha 2 (win+linux)

[N. W. Perry]

That's not the behavior I've experienced. If I select something on the model and hit Ins, it'll duplicate whatever I have selected

Same here; I would also say it depends what is selected, and where you try to Insert it.

If nothing is selected you'll get the behavior Roland describes, but if things are selected you get a copy of them. (Of course, if parts are selected, then one of them is going to be the working part anyway.)