Are you considering the "longest" chain to be the one with the greater height? Generally with PoS (and possibly slimcoin PoW - I don't know much about how it works) the important variable is trust, not height.

For example, I just had a quick look at debug.log and a recent PoW block increased trust by 11 million, while a PoS block increased it by 39 million. So a fork with (say) 10 PoW blocks would have a greater height, but a fork with 5 PoS blocks would have greater trust. That one is the longer chain.