Operating system: Linux-4.15.0-121-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce RTX 2060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 450.80.02
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: rB3e85bb34d0d7
Worked: (newest version of Blender that worked as expected)
Short description of error
Switched off constraints corrupt movement of bones and animation afterwards. Constraints which is switched off shouldn't influence the animation process. Animator need way to switch between different phases. For example, now I need my hand as a parent of weapon, later I need vice versa. But Blender making cycle dependency even when constraint is off.
Exact steps for others to reproduce the error
Open my blend file, select "IK" bone, Press G, drag it away, click Right Mouse Button, attention to weird behavior. After this delete constraint from "Weapon" bone and try again from the beginning.