For reinitialization of state variables after preequilibration, we need to add fixed parameters for initial conditions (otherwise parameter values can't be different for pre-equilibration and the following period). This case was handled fine.
If we want to estimate initial conditions and want to compute sensitivities w.r.t. those, we need non-fixed parameters for the initial conditions. This was not handled correctly, those were added as fixed parameters.
As a consequence, we can't handle reinitialization and estimation of initial values for the same state variable.
Closes #2455.