What if you actually only wish to only change the sample for a single partial without changing anything else?
I see no bugs in the fact, that just selecting a new sample, in it self does'nt delete anything except the previous sample sound.
You can start out with a clean "Simple Sine" preset if you wish to build a preset from the ground.
I agree it could be great and a good tool, if you had reset buttons to both reset the full partial and to reset the partials engine parameters only.
Instead at the time being, it seems like you can copy a clean partial from the current or from another preset and paste it to a partial in any preset you wish. Just remember to save any current work in a preset before changing presets. (That's imho a quite powerful feature, as you can copy any partial to another this way.)
But yes a press on a simple button would make it easier to clean the full partial or the engine parameters in a partial.
If a clean partial is avalble, you can just use that to add new samples, and then turn down the volume for the partials you don't use in the mixer or mute them.
You can also remove for example Mixer settings for a partial manually. You can do that with any settings for a partial.
The modulation you talk about can be the FM Mod amount set for the current partial.
Keep in mind that all partials in use for the presets will blend to a sound. That's the idea.
I have not checked for bugs in theese things yet. But just changing a sample should not delete anything else automaticly, as you perhaps would like to keep all settings for the new sample.
Selecting a new sample is not like shifting a synclavier preset. You select a sample for a single partial. You have 12 partials, and thus you can select up to 12 samples for a single preset. One for each partial. That you could'nt, if you reset the full preset each time you select a sample.
The fact you can hear the sample before you select it for a sound, make it possible to hear how it sounds clean without the partials settings.
Does this explain it?
Please report back if you find, that the mentioned functions does'nt work.