I've recently stumbled upon Caustic, and overall I'm very impressed, most of all by the user interface that's really fun to play with. The tutorial videos are also really great and help one get productive in no time.
Now I'm trying to create an ambient style track, and the thing I'm fighting with at the moment is a rather annoying "wobbling" effect audible in many PadSynth configurations, as if from an LFO controlling the volume. This is pretty easy to reproduce: Create a new PadSynth, go to harmonic table 1, draw in a single harmonic. Depending on the value of the (yellow) bandwidth bar, the volume will oscillate at different frequencies. I've compared this with the PADsynth in Yoshimi (a fork of ZynAddSubFx), which seems to be based on the same algorithm; there, the same effect is also noticeable, but less pronounced, and less annoying.
After skimming the description of the algorithm, my best guess as to what is happening is this: Mixing two similar frequencies will always produce a beat due to interference, but as the ZynAddSubFx implementation shows, with more than two frequencies the effect can be made to cancel out to some extent. The regularity and reproducibility of the beat patterns in Caustic suggests that either the phases of the frequencies belonging to harmonic are not randomized properly, or there are too few frequencies per harmonic (maybe because the spectrum array fed into the FFT is too small). In any case, this should be relatively easy to fix (possibly by adding an HQ switch if the fix is computationally too challenging for some devices).