Satisfiability in propositional logic is well researched and many approaches to checking and solving exist. In infinitevalued or fuzzy logics, however, there have only recently been attempts at developing methods for solving satisfiability. In this paper, we propose new benchmark problems and analyse the function landscape of different problem classes, focussing our analysis on plateaus. Based on this study, we develop Mixing CMA-ES (M-CMA-ES), an extension to CMA-ES that is well suited to solving problems with many large plateaus. We empirically show the relation between certain function landscape properties and M-CMA-ES performance.