The reason for this kind of effects is the nonlinearity in the analog filters. The saturation effects introduce chaotic behaviour to the filters. This makes them interesting to experiment with.
It affects all filters with nonlinear elements. In Icarus this are the anlog types (Cartis, analog, scream, 303, Tone2, Butter) and the Fractal types.
The sound of the filter does also depend on the volume of the osciallators