Hi Mark, so far I have not heard of any other reports similar to this.

It sounds like you may be able to reproduce the problem from a particular file, though?

If so, can you please send it to me, you can e-mail it to me at moi@moi3d.com if you want to keep it private.

What kind of tweak causes the problem? Is it when some curves that were originally used to create the surface are edited in some particular way? It is possible that you are seeing some result of the history update mechanism that remembers how a surface was constructed, and will reconstruct it if input curves are modified.

If that is the problem, you can select the surface and turn off history updating on it by selecting it and going to Edit / History / Disable update. That would then prevent the surface from recalculating when the input curves are modified.

- Michael