Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 760/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.15
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: rB26bd5ebd42e3
1- Create a sphere.
2- Select some of its polygons and duplicate them.
3- Separate the duplicated polygons as a separate object.
4- Add a shrink wrap mod to the separated object and try to shrink wrap it to the original sphere you created or any other object for that matter.
5- Nothing will happen and no mod controls are effective!
6- This is due to the fact that the extracted object has the exact same topology with its original. Try shrink-wrapping the same extracted object on a different object, the modifier works as expected.