Parameter initial conditions broken for `DiscreteProblem`s

[TorkelE]

using ModelingToolkit, JumpProcesses
using ModelingToolkit: t_nounits as t

# Works.
let
    @parameters β γ
    @variables S(t) I(t) R(t)
    rate₁   = β*S*I
    affect₁ = [S ~ S - 1, I ~ I + 1]
    rate₂   = γ*I
    affect₂ = [I ~ I - 1, R ~ R + 1]
    j₁      = ConstantRateJump(rate₁,affect₁)
    j₂      = ConstantRateJump(rate₂,affect₂)
    j₃      = MassActionJump(2*β+γ, [R => 1], [S => 1, R => -1])
    @mtkbuild js      = JumpSystem([j₁,j₂,j₃], t, [S,I,R], [β,γ])

    u0s = [S => 999, I => 1, R => 0]
    ps = [β => 0.01, γ => 0.001]
    dprob = DiscreteProblem(js, u0s, (0.0, 10.0), ps)
end

# Errors.
let
    @parameters β γ S0
    @variables S(t) = S0 I(t) R(t)
    rate₁   = β*S*I
    affect₁ = [S ~ S - 1, I ~ I + 1]
    rate₂   = γ*I
    affect₂ = [I ~ I - 1, R ~ R + 1]
    j₁      = ConstantRateJump(rate₁,affect₁)
    j₂      = ConstantRateJump(rate₂,affect₂)
    j₃      = MassActionJump(2*β+γ, [R => 1], [S => 1, R => -1])
    @mtkbuild js      = JumpSystem([j₁,j₂,j₃], t, [S,I,R], [β,γ])

    u0s = [I => 1, R => 0]
    ps = [S0 => 999, β => 0.01, γ => 0.001]
    dprob = DiscreteProblem(js, u0s, (0.0, 10.0), ps) # ERROR: MethodError: no method matching unhack_observed(::Vector{Equation}, ::RecursiveArrayTools.ArrayPartition{Any, Tuple{Vector{MassActionJump}, Vector{ConstantRateJump}, Vector{VariableRateJump}, Vector{Equation}}})
end

ERROR: MethodError: no method matching unhack_observed(::Vector{Equation}, ::RecursiveArrayTools.ArrayPartition{Any, Tuple{…}})
The function `unhack_observed` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  unhack_observed(::Vector{Equation}, ::Vector{Equation})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/nonlinear/initializesystem.jl:352

Stacktrace:
  [1] generate_initializesystem(sys::JumpSystem{…}; u0map::Dict{…}, pmap::Dict{…}, initialization_eqs::Vector{…}, guesses::Dict{…}, default_dd_guess::Float64, algebraic_only::Bool, check_units::Bool, check_defguess::Bool, name::Symbol, extra_metadata::@NamedTuple{…}, kwargs::@Kwargs{})
    @ ModelingToolkit ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/nonlinear/initializesystem.jl:17
  [2] generate_initializesystem
    @ ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/nonlinear/initializesystem.jl:6 [inlined]
  [3] ModelingToolkit.InitializationProblem{…}(sys::JumpSystem{…}, t::Float64, u0map::Dict{…}, parammap::Dict{…}; guesses::Dict{…}, check_length::Bool, warn_initialize_determined::Bool, initialization_eqs::Vector{…}, fully_determined::Nothing, check_units::Bool, use_scc::Bool, kwargs::@Kwargs{…})
    @ ModelingToolkit ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/diffeqs/abstractodesystem.jl:1307
  [4] InitializationProblem
    @ ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/diffeqs/abstractodesystem.jl:1285 [inlined]
  [5] #_#1075
    @ ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/diffeqs/abstractodesystem.jl:1263 [inlined]
  [6] InitializationProblem
    @ ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/diffeqs/abstractodesystem.jl:1262 [inlined]
  [7] #InitializationProblem#1073
    @ ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/diffeqs/abstractodesystem.jl:1251 [inlined]
  [8] InitializationProblem
    @ ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/diffeqs/abstractodesystem.jl:1250 [inlined]
  [9] maybe_build_initialization_problem(sys::JumpSystem{…}, op::Dict{…}, u0map::Dict{…}, pmap::Dict{…}, t::Float64, defs::Dict{…}, guesses::Dict{…}, missing_unknowns::Set{…}; implicit_dae::Bool, kwargs::@Kwargs{…})
    @ ModelingToolkit ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/problem_utils.jl:546
 [10] maybe_build_initialization_problem
    @ ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/problem_utils.jl:526 [inlined]
 [11] process_SciMLProblem(constructor::Type, sys::JumpSystem{…}, u0map::Vector{…}, pmap::Vector{…}; build_initializeprob::Bool, implicit_dae::Bool, t::Float64, guesses::Dict{…}, warn_initialize_determined::Bool, initialization_eqs::Vector{…}, eval_expression::Bool, eval_module::Module, fully_determined::Nothing, check_initialization_units::Bool, tofloat::Bool, use_union::Bool, u0_constructor::typeof(identity), du0map::Nothing, check_length::Bool, symbolic_u0::Bool, warn_cyclic_dependency::Bool, circular_dependency_max_cycle_length::Int64, circular_dependency_max_cycles::Int64, substitution_limit::Int64, use_scc::Bool, kwargs::@Kwargs{})
    @ ModelingToolkit ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/problem_utils.jl:669
 [12] DiscreteProblem(sys::JumpSystem{…}, u0map::Vector{…}, tspan::Tuple{…}, parammap::Vector{…}; use_union::Bool, eval_expression::Bool, eval_module::Module, kwargs::@Kwargs{})
    @ ModelingToolkit ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/jumps/jumpsystem.jl:428
 [13] DiscreteProblem(sys::JumpSystem{…}, u0map::Vector{…}, tspan::Tuple{…}, parammap::Vector{…})
    @ ModelingToolkit ~/.julia/packages/ModelingToolkit/iQ7So/src/systems/jumps/jumpsystem.jl:414
 [14] top-level scope
    @ ~/Desktop/Julia Playground/Environment - Catalyst only/catalyst_playground.jl:39
Some type information was truncated. Use `show(err)` to see complete types.

Other problem types seems to be fine.