In the VanDerPol Reference FMU 3.0 XML

der(x0) = x1
der(x1) = mu * ((1 - x0 * x0) * x1) - x0

the parameter mu has a valueReference="5" but is not listed in any dependencies, which according to the standard means
"For a real valued unknown and a real valued known, if the known is not listed among the dependencies then the partial derivative of the unknown with respect to that known is identically zero."
The reference implementation accordingly returns zero for all partial derivatives wrt. to variables being not a state, e.g. parameter mu. But this is wrong for the VanDerPol oscillator, if e.g. requesting the partial derivative of der(x1) wrt. mu.
I would prefer either to return the correct value or an error message when requesting the partial derivative of der(x1) wrt. mu.

Taken from here.