SemilinearODEProblem errors when quadratic terms are present #4257

using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D

@variables x(t) = 0.1 y(t) = 0.1 z(t) = 0.1
@parameters σ = 10.0 ρ = 28.0 β = 8 / 3

eqs_1 = [
    D(x) ~ σ * (y - x),
    D(y) ~ x * (ρ - z) - y,
    D(z) ~ x * y - β * z,
]

eqs_2 = [
    D(x) ~ σ * (y - x),
    D(y) ~ x * (ρ - 0) - y,
    D(z) ~ 0*x * y - β * z,
] # No quadratic term here

@mtkcompile sys_1 = System(eqs_1, t)
@mtkcompile sys_2 = System(eqs_2, t)

prob_1 = SemilinearODEProblem(sys_1, nothing, (0.0, 10.0)) # Errors 
prob_2 = SemilinearODEProblem(sys_2, nothing, (0.0, 10.0)) # Works

julia> show(err)
1-element ExceptionStack:
LoadError: ArgumentError: System sys_1: variable quadratic_Bₘₜₖ_3 does not exist
Stacktrace:
  [1] getvar(sys::System, name::Symbol; namespace::Bool)
    @ ModelingToolkitBase ~/.julia/packages/ModelingToolkitBase/7DETx/src/systems/abstractsystem.jl:1124
  [2] getproperty(sys::System, name::Symbol; namespace::Bool)
    @ ModelingToolkitBase ~/.julia/packages/ModelingToolkitBase/7DETx/src/systems/abstractsystem.jl:1065
  [3] getproperty(sys::System, name::Symbol; namespace::Bool) (repeats 2 times)
    @ ModelingToolkitBase ~/.julia/packages/ModelingToolkitBase/7DETx/src/systems/abstractsystem.jl:1063
  [4] getproperty(sys::System, name::Symbol)
    @ ModelingToolkitBase ~/.julia/packages/ModelingToolkitBase/7DETx/src/systems/abstractsystem.jl:1059
  [5] (::ModelingToolkit.var"#82#83")(i::Int64)
    @ ModelingToolkit ./none:-1
  [6] iterate
    @ ./generator.jl:48 [inlined]
  [7] collect_to!(dest::Vector{SymbolicUtils.BasicSymbolicImpl.var"typeof(BasicSymbolicImpl)"{SymReal}}, itr::Base.Generator{UnitRange{Int64}, ModelingToolkit.var"#82#83"}, offs::Int64, st::Int64)
    @ Base ./array.jl:848
  [8] collect_to_with_first!(dest::Vector{SymbolicUtils.BasicSymbolicImpl.var"typeof(BasicSymbolicImpl)"{SymReal}}, v1::SymbolicUtils.BasicSymbolicImpl.var"typeof(BasicSymbolicImpl)"{SymReal}, itr::Base.Generator{UnitRange{Int64}, ModelingToolkit.var"#82#83"}, st::Int64)
    @ Base ./array.jl:826
  [9] collect(itr::Base.Generator{UnitRange{Int64}, ModelingToolkit.var"#82#83"})
    @ Base ./array.jl:800
 [10] SemilinearODEProblem{true, SciMLBase.FullSpecialize}(sys::System, op::Nothing, tspan::Tuple{Float64, Float64}; check_compatibility::Bool, u0_eltype::Nothing, expression::Type, callback::Nothing, sparse::Bool, stiff_linear::Bool, stiff_quadratic::Bool, stiff_nonlinear::Bool, jac::Bool, kwargs::@Kwargs{})
    @ ModelingToolkit ~/.julia/packages/ModelingToolkit/dBZDD/src/problems/semilinearodeproblem.jl:98
 [11] SemilinearODEProblem
    @ ~/.julia/packages/ModelingToolkit/dBZDD/src/problems/semilinearodeproblem.jl:69 [inlined]
 [12] SemilinearODEProblem
    @ ./none:-1 [inlined]
 [13] SemilinearODEProblem(sys::System, op::Nothing, tspan::Tuple{Float64, Float64})
    @ ModelingToolkit ./none:-1

(jl_AEuYml) pkg> st
Status `/tmp/jl_AEuYml/Project.toml`
  [961ee093] ModelingToolkit v11.9.0

julia> versioninfo()
Julia Version 1.12.4
Commit 01a2eadb047 (2026-01-06 16:56 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 64 × AMD Ryzen Threadripper 3970X 32-Core Processor
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, znver2)
  GC: Built with stock GC
Threads: 1 default, 1 interactive, 1 GC (on 64 virtual cores)
Environment:
  JULIA_EDITOR = code
  JULIA_VSCODE_REPL = 1
  JULIA_PKG_USE_CLI_GIT = true