0) default blender scene
1) set a key for the cube (e.g. location)
2) advance a few frames, move the cube and set another key
3) in object panel (in properties editor) calculate Motion Path
4) try to move the object, it doesn't work

It seems to me that automatic recalculation is never working. Even though in both bones and objects code we are explicitly trying to recalculate the paths.
So to work that around I did this change:

\bf\source\blender\editors\transform\transform_conversions.c
around 5069::

if (C && recalcObPaths) {
//ED_objects_clear_paths(C); // XXX for now, don't need to clear
-ED_objects_recalculate_paths(C, t->scene);
+//ED_objects_recalculate_paths(C, t->scene);
}

It solves the immediate issue (locking down of location). But is no where close to address the real one (automatic recalculation broken).
(attached file reproduces this problem)