I started a thread on it here.
Basically, what I've found is that drag-copy and delete seem to work much better with large scale objects than take and take-copy, at least for me.
Although I've used the take-copy pie menu many times for large builds in the past, recently it hasn't been working for me. No matter what I do, some parts of the build are missing.
Through experimentation, I discovered that I could actually see this process visually using the take pie menu option. When I try to take a large build, I can actually see part of it disappear into inventory, while other parts of it remain in world selected.
Perhaps the most amazing thing is that drag-copy still works flawlessly for me. And after much head-banging, I discovered that delete also works for me on large builds.
So, I developed a workaround in which I use delete to copy a large build into inventory!

I'm posting here to raise general awareness of the issue among both residents and Lindens.
Not sure if take and take-copy are bugged, but there is definitely something about them that causes them to scale less well than the alternatives.
Anyway, see my thread above for more details.