Variable is not a function of independent variable error for trivial example

[oameye]

I am trying out the ModelingToolkit.jl package and I get this weird error when defing the classical harmonic oscillator with the following code

using ModelingToolkit,
@variables t x(t)
@parameters ω₀
Dₜ = Differential(t)
@named sys = ODESystem([Dₜ(Dₜ(x)) + ω₀^2*x ~ 0])

It produces the error

ArgumentError: Variable x(t) is not a function of independent variable (ω₀^2)*x(t).

I do not understand the where the error comes from. Just putting the second term on the other side gets rid of the error, i.e.

using ModelingToolkit,
@variables t x(t)
@parameters ω₀
Dₜ = Differential(t)
@named sys = ODESystem([Dₜ(Dₜ(x)) ~ - ω₀^2*x])

runs just fine. My apologies if this error comes from my lack of understanding how the package must be used.

[YingboMa]

It should be @named sys = ODESystem([Dₜ(Dₜ(x)) + ω₀^2*x ~ 0], t, [x], [ω₀])

[ChrisRackauckas]

Why does the automatic detection of states and parameters fail here? Seems like a reasonable case for it to work?