The magnets on V4 act like JCM's on V3, but work better. Magnetising them to each piece of clothing makes the clothing work better as well (in 99.9% of cases).
To make Poser work correctly, you should load V4, make sure she is selected, then load a piece of clothing and use magnetise (the first magnetise that has no numbers). Re-select V4, then load another piece of clothing and magnetise using the same one as before. Etc, etc.
Always make sure you have V4 selected before you load each piece of clothing, as this makes crosstalk work correctly.