Why can't I build a copyable object?

It is my land, my objects.
The object in question is modifiable and copyable but not transferable because one of the many items in its Contents is not transferable.
I can build it from my inventory with no problem, just drag it on land.
If I create a cube and put this item in the contents of the cube, why can't I drag it from the cube contents to land?
If I put transferable objects in the box, they can be rezzed OK.
Why can't my object with COPY rights be rezzed from the contents of a box I own on to my land?

It may sound a little weird, but when you put Object A into the contents of Object B, A becomes B's property. Dragging the non-transferrable A to the ground directly from B's inventory would constitute a transfer of ownership (from B to you), as far as the system is concerned, so it doesn't allow it. The logic doesn't hold completely, since you can of course pull the item back out into your inventory, which is just as much a transfer of ownership, but that's the logic, nonetheless.

OK thanks. What makes it even more confusing is although I can't move the object from B to my land manually, B CAN REZ it on my land using script so I put a touch_start script in it. It is still copyable and modifiable and still no transfer. I fail to see the obscure ownership security involved but presumably there is a loophole being covered somewhere.