Graph of derivative (Function app)

[ThomasA]

Hello,
why does the app not find an extremum?
Here is what I entered:
In symb view: F1(X)= x*(x-3)*(x+4)
F2(x)= d F1(X)/d(X) (On the calc I used the template for the partial derivative)
In plot view the graphs of F1 and F2 are displayed. Using the menu and Fcn I analyze the graph of F1. The app finds roots and extrema (ok). Then I put the cursor on the graph of F2 (parabola). Now the app finds the roots but not the extremum (minimum in this case) (not ok) . The roots are no problem (ok). For a test I changed F2 to F2(X) = -(X+1)^2 to mimic the parabola - this time the app is successful and finds the maximum and the roots. (ok).
So - is there a problem with a function defined in terms of a derivative?
Thomas

(P.S. I am using the latest firmware)