Like this?

There are two answers.  The technical answer is to; Spawn a Morph Target, delete the magnet,  return all other morphs to a value of "Zero," and then set the new morph to a value of "1."  This really follows the premise that there were no other morphs "On" when you created the magnet, though.  That is how magnets are supposed to be created, as a Deformer to the original shape of a mesh(Without any other Magnets, or morphs, active.)  Obviously, though, you need'nt be at that point when you do create a magnet...

Anyhow, I do'nt always like Consolidating all of my Morphs, and Magnets, into one dial.  Hence the reason I leave magnets alone once I'm done creating;  although I do run into the same problem you are having.  To answer your question, click:

Display > Deformers > Hide All.

This should be a permanent toggle, but each time you select a new body part, with magnets, you need to repeat the step.

Add Element to Deform is there because you only Create a Magnet from particular a single/particular Figure Part; hence that magnet will only effect the Part it was created with.  If your Magnet Zone is actually large enough to touch other Parts, that you would also like it to effect, then you need to add those parts to the Magnet Set(From there at the Properties of the Magnet Zone.)