Question: Wrong Killing vectors using DifferentialGeometry:-Tensor package

I need to find the Killing vectors of a metric.

I initiate the session as

> restart;
> with(DifferentialGeometry); with(Tensor); with(LieAlgebras);
> DGsetup([t, r, z, phi], M);

and enter my metric as

M > g1 := evalDG(-dt &t dt ...);

I do not have an unknown function in my metric but I have two free parameters (e.g. a and b).

I use

M > K1 := KillingVectors(g1, parameters = [a, b]);

to find the Killing vectors (I also tried without giving the parameters). It finds some vectors but when I run

M > L1 := map(LieDerivative, K1[3], g1);

or for other members of K1, I cannot get zero but (a=a, b=b) case should give all zero.

I tried with some other metrics and got zero as it should be. I am sure that my metric is correct.

Is there any chance that Maple misses something, or better, am I missing something?

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