I hesitate to call this a bug, but... see what you think. I came across this while texturing the workshop scene. To try it out, texture a sphere with the 'colored glass 3' material, then edit the material, and go into the function editor. Delete the turbulence node and the now-redundant link (this is just for clarity). Now the node preview looks like this:

Next, alter the noise type to 'Perlin Noises/Value' and as expected the node changes, in this case to:

Now change back to 'Perlin Noises/Gradient'. What you get then is this:

The node is different even though the parameter values are all the same! To get an approximation to the original you need to alter the wavelength z value to about 0.2:

I can't see why this would happen - anyone have any thoughts?

This could be a problem with initializing function values. I would let e-onsoftware's tech support know about this.

The function editor is famous for this sort of thing when working with procedural terrains.

Thanks, I'll do as you suggest and let e-on know. It's the first time I've come across this, but then I haven't got very deep into the workings of the function editor yet :-)