Hi thanks for posting this.
I've logged a bug report for this. The real problem I see is not being able to undo after zero was entered. Otherwise, I'm afraid it might be as design, because there may be a limit to the logic of Sculpt scaling.
Here's why: this is a direct environment, it's not parametric. Every time you see a preview of a change you've made to the form you are working on, it's a freshly drawn body. The zero scaled appearance is really the state of the model at that point, ergo, how do you scale a bunch of combined points? This is akin to placing Sketch Points one on top of the other and then using sketch > scale. How would Sketch move those points apart if they are combined?
Therefore, undo should be your avenue out of the problem. That is the reason we allow mid-command undo while in edit form. But undo is not doing the job here, thus it's the bug.
Anyway here is your workaround:
1. Type faster
2. Don't use a zero before the decimal. You can easily type in ".5698" without the zero and it takes the same effort to click into the box, just remove the zero when you do that.
Thanks again,
Phil Eichmiller
Software Engineer
Quality Assurance
Autodesk, Inc.