So - this gets weirder every time I do something!
Here’s your file back, just press Play and watch…
ro038_sl363_t01_20180226xxx.blend (602 KB)
What I did was to add another bone and make it copy location and rotation of the green cube. Then your other bone stops misbehaving - I have not the slightest possible explanation as to why this is. If I turn off the constraints - the eye icons, it still behaves itself. If I just add a new bone and do nothing with it, your bone misbehaves???
I remain totally perplexed, as I don’t have the movie clip I cannot try a new bone with the same solver - it just does nothing, but any other object using the green cubes solver seems to work - perhaps you can only use the solver once in a project, then use this object to drive everything else that would need this solver? I am clutching at straws here and the manual is about as much use as a chocolate teapot on advanced procedures!