Symbolic formulas for initial conditions being dropped

[isaacsas]

It seems that maybe symbolic initial condition expressions are being substituted for numeric values instead of letting ModelingToolkit handle this downstream, which prevents users from remakeing problems easily, see

https://discourse.julialang.org/t/performing-global-sensitivity-analysis-on-a-big-reaction-network-imported-as-a-sbml-file/93000/14