Having a 1way link will boost your PR of course, but what if this page is holding lots of links like gambling or other not webmaster related websites. Is this good for you webmaster related website?
Plus how did that site got a pr 7? It looks suspicious to me.
I think its because a ony way link from the PR8 postnuke website... I checked the websites which having a link from this site (the first ones), there is no website with a pagerank of 6 (3,4 and 5)