I already duplicated that effect in one of my sheets as desribed in my answer above.
I deleted all which seems having no effect and am now left with the data definitions, definition of function, guess vector and call of genfit and at last the eval of the guess vector.
If I delete the last 1 in the definition of the guess vector, genfit fails and the eval of vg2 shows the correct values. If I add the 1 the same weird effect is shown.
It looks like genfit() somehow modifies the guessvector on the worksheet level.
This time it matters if vg2 is evaluated before or after genfit(). (In your last sheet I think it did not matter!?)
