`derivative` does not respect boundary condition

[SimonEnsemble]

I'm using bc="nearest" for my 1D spline interpolator, but the derivative function is not respecting this boundary condition.
here, I'm showing that the derivative is nonzero, whereas the interpolator is flat in this region of the domain.

[SimonEnsemble]

(for now, using Calculus.derivative instead of derivative in this package)