OS/X High Sierra, MacBook Pro current
Short description of error
Usability – obvious-in-retrospect "follow path" mistake not caught
Exact steps for others to reproduce the error
Create an object and a path, then set a "follow path" constraint. Click on the path, and in "Object Data" specify the Evaluation Time but ("I plead n00b1e innocence!") fail to realize the importance of also specifying a non-zero value for Frames
Well, the resulting system behaviors are "genuinely 'WTF?!?!'" (Try it .. you'll see what I mean..)
When I clicked on "Animate Path," Blender sort-of correctly told me that "the path was already animated," but actually it wasn't – because it is nonsensical for either or both of these parameters to be zero. (Oops.) This would have been a stupendous time to alert me to this.
If there are no keyframes, and if the present set of parameters is nonsensical (frames=0), then I think that the software should stop and throw a meaningful exception.