1. Open Impress, new or existing document, select any object
2. Go to sidebar, animations deck
3. Click "Add" to add animation
4. Change animation category to "Motion paths"
5. Select any of the available motion paths
6. Finally, select another motion path, different from the first one
After step 6, the new motion path gets activated (this is clearly visible when instant preview of animations is on, the object moves to follow the new motion path ... if no instant preview, it is obvious after starting the slideshow). However, the old motion path present after step 5 as outlined by thin grey dashed line remains on the slide
The thin grey dashed line representing the motion path updates accordingly
Afaics, this has always (at least since the sidebar has been introduced) been the case
Yes, it is old.
*** This bug has been marked as a duplicate of bug 33022 ***