XLock prevents crosstalk between magnets.  If you're doing separate magnets for the clothes and the figure, apply the xlock to the figure before you create the magnets for the clothes.  I generally apply the XLock to the figure immediately after I create the magnets for it, just in case I decide to use separate magnets for clothes later.  You should probably just get in the habit of doing that every time you use the set - I've never known it to cause any problems.

The double feed thing should work for you when you encounter the problem you're seeing.  I forget which figure (person or clothing) you need to have selected when you apply the double feed fix pose, so try it on both, but one or the other should solve that problem.

I get the figure freeze occasionaly myself, but for me it turns out the figure isn't really frozen, the screen just doesn't update for changes unless I select something else.  I find setting a camera dot in that situation usually updates the screen with your adjustments.  It's still a hassle though since you can't see your changes in "real time."  I think it's more of a Poser error than a problem with the magnet set, but I'm not certain what it is about the magnet set that exposes this Poser error.  Nothing seems to remove the problem either short of creating a new scene.

Hope this helps some.