The text presents two case studies from the area of Polish middle voice morpho-syntax. One case concerns anticausatives formed with the particle się and their simpler counterparts based on identical roots. The other – "clear" alternating frame verbs, their prefixed correspondents and middle formations based on the same roots. The first case strikes us as problematic for both modern approaches to morpho-syntax in generative grammar – the lexicalist approach and the root based construction approach. It turns out to be problematic for the first model only, if certain proposals (in particular Alexiadou and Doron 2012) concerning non-active morpho-syntax are discarded. The second case shows, however, that certain data cannot be explained within the root based grammar, while the lexicalist mechanisms account for them naturally. Polish morpho-syntax calls for introducing clear demarcation lines between the data that can be rendered by syntactic mechanisms and such which require lexical analyses and "productivity" of the data cannot provide such a boundary. They need to be drawn on an empirical basis.