I tested this on multiple Blender versions and it happened in all of them.
So, a clarifying GIF:
For some reason the animation I have done to an original mesh object messes up the show/hide-toggle animation functionality of separated new meshes and the original mesh.
- I separate part of a mesh from a particular object to a new object
- Animate that new object's show/hide-toggle
- The show/hide-toggle animation is automatically duplicated to the original mesh-object's show/hide-toggle as well (not desired, faulty action, bug)
- I remove the object's translate-animation curve
- This won't happen and the show/hide-toggle animation works as expected