fix simplify

Author: vyudu

src/systems/systems.jl

@@ -151,11 +151,13 @@ function __structural_simplify(sys::AbstractSystem, io = nothing; simplify = fal
         end
 
         noise_eqs = StructuralTransformations.tearing_substitute_expr(ode_sys, noise_eqs)
-        return SDESystem(Vector{Equation}(full_equations(ode_sys)), noise_eqs,
+        ssys = SDESystem(Vector{Equation}(full_equations(ode_sys)), noise_eqs,
             get_iv(ode_sys), unknowns(ode_sys), parameters(ode_sys);
             name = nameof(ode_sys), is_scalar_noise, observed = observed(ode_sys), defaults = defaults(sys),
             parameter_dependencies = parameter_dependencies(sys), assertions = assertions(sys),
-            guesses = guesses(sys), initialization_eqs = initialization_equations(sys), tearing_state = get_tearing_state(ode_sys))
+            guesses = guesses(sys), initialization_eqs = initialization_equations(sys))
+        @set! ssys.tearing_state = get_tearing_state(ode_sys)
+        return ssys
     end
 end