Question: Problem with plot

In this code, plot() and Norm() fail when used over a piecewise() function:

Error, invalid input: VectorCalculus:-Norm expects its 1st argument, v, to be of type {Matrix, Vector}, but received piecewise(t < 0, Vector[row](2, {(1) = -1, (2) = 0}, attributes = [coords = cartesian]), Vector[row](2, {(1) = 1, (2) = 0}, attributes = [coords = cartesian]))

Note that the same Norm() and piecewise() work fine when used without the plot() function:

Norm(vec(1));
                               1

Code works fine when piecewise() is removed, leaving a plot() / Norm() combination, for example:

So only the simultaneous combination plot() / Norm() / piecewise() fails. 

Finally, the question is:

Is there a way to plot Norm() / piecewise() combinations without workarounds like intermediate PLOT structures?

Thank you