The details of this particular suit are, as is the case with many such legal actions between rivals, terribly complicated. Short version: Funimation claims ADV (now Sentai) owes money through a third-party licensor which ADV was previously indebted to.
Opinions are divided as to whether this is a sleazy cash-grab by Funimation or a sleazy dodge by Sentai. Neither option looks particularly appealing.
Sum of comment: when you're dealing with legal spats in fandom, the lawyers are the only winners.
– Serdar Yegulalp