I don't think that those results are unexpected. Afterall, adaptivness isn't meant to speed up rendering, it just helps to distribute noise more evenly over entire image. So, if you have situation where there's good mix of areas which tends to hide noise pretty well, with areas where's noise is very evident even in low quantities, then adaptivity might be just counterproductive. So if you have rendering of house with big flat walls in the forest or in meadows, or nicely lit interior scene with big windows and even bigger hairy carpets, in that situation adaptivity may do more harm than good. I guess it isn't so universal thing, as we hoped it to be. Maybe decision to hide its controls, wasn't the best one?
What puzzles me more, is how adaptivity reacts to brigtness in diffuse texture. It assigns much more samples to darker textures than to brighter ones. You can clearly see that in first post in the striped wall part.