System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 425.31

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-03-10 09:25, hash: rB87fa2d143d1e

Short description of error
Link-duplicated Curves (alt-D) are somehow creating dependencies to the original Curve if a Hook modifier is attached to the original. It seems the Duplicates mirror the original Curve along with the Hook dependency, regardless if they have a Hook modifier on their own.
I also had trouble to assign a new Hook modifier on one of these copied Curves. They are not responding at all, even if no other Hook modifier is attached in the scene.

Exact steps for others to reproduce the error