I know this is an old question, but for the benefit of new readers...
In PowerPoint 2016 I have been struggling with this issue for a couple of hours now. I have found no means of disabling this snapping of motion points to motion points of other objects - particularly an end-point snapping to a start-point of another object.
Here is my work-around:
- Cut the object, which you are currently animating, and paste it into a new temporary slide
- On the temporary slide, edit your animation paths to your heart's desire
- Copy/cut your object from the temporary slide back to the original slide
Now the animation path points of your object should have been placed in the exact same positions as you set them on the temporary slide.
Note: Using the keyboard shortcuts for cut/copy/paste (CTRL+X / CTRL+C / CTRL+V) among slides will place your objects at the same position on the target slide, as they were on the source slide, so you do not need to worry about getting the position right on the destination slide.