Strange `DEF` parameter appears in `parameter(sys)` for certain systems

[TorkelE]

When you call get_parent of a DAE with a subsystem is one case I have found (but I think it might hold for systems with subsystems generally):

using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D
@parameters p d
@variables X(t)
eqs_bot = [
    D(X) ~ p - d*X
]
eqs_top = [
    D(X) ~ p - d*X,
    X^3 ~ log(X + Y) - Y^2 + 3.0
]
@named osys_bot = ODESystem(eqs_bot, t)
@mtkbuild osys = ODESystem(eqs, t; systems = [osys_bot])
psys = ModelingToolkit.get_parent(osys)
parameters(psys)

p
 DEF
 d
 osys_bot₊p
 osys_bot₊d

What is this DEF parameter? Also, seems internal, shouldn't parameters filter it out?

[ChrisRackauckas]

That is a bug, should be fixed by #3403

[TorkelE]

👍

[TorkelE]

Closed as this is a replicate of #3401