Question: Matrices in Physics package

Hello! I try to make friends physics package and matrixes. But I am faced with difficulties. To be more specific, to consider a code:

Setup(mathematicalnotation = true);
Setup(tensors = A[mu](X));
PDEtools:-declare(A(X), p0(X), pm(X), pp(X), pt(X), U(X), m5(X))

And then I create a matrix:

pt := proc (X) options operator, arrow; Matrix(2, 2, [[p0(X), sqrt(2)*pp(X)], [sqrt(2)*pm(X), -p0(X)]]) end proc;

It displays as:

Why do p0, pp, pm become function only one variable x1?

Interestingly that maple understands the next matrix:

Nevertheless even for function only one variable derivative works fine:

And I can construct more complicated functions:

But why is only one variable?

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