indeed mxmonitor and leech hammer open the whois windows to get user information, they do hide the actual whois windows but unfortunately are not able to remove them from the list of open windows in winmx
btw, the problem of winmx jumping up and down as they open and close is quite easy to overcome, leave a single whois window open - then the others will just open next to it, and not cause it to keep jumping up and down (unless it gets down to the second row anyway)