Media9 error with two .vws files

Question

I've tried to include a second U3D model to my document and got the following error:

! LaTeX error: "kernel/command-already-defined"
! 
! Control sequence \l_mix_vfile_stream already defined.

The (minimal) code to include the models is:

% COMPILED WITH PDF LATEX
% USING THE UP-TO-DATE VERSIONS OF media9 AND l3kernel
\documentclass[ a4paper, 11pt, twoside, openleft ]{book}
\usepackage[dvipdfmx]{media9}

\begin{document}
% Include model1
\includemedia[%
activate=onclick,%
deactivate=pageinvisible,%
3Dviews=model1.vws]{}%
{model1.u3d}% Binary file
% Include model2
\includemedia[%
activate=onclick,%
deactivate=pageinvisible,%
3Dviews=model2.vws]{}%
{model2.u3d}% Binary file
\end{document}

.u3d files are binary and the .vws looks like:

% modelX.vws - Nothing special here.
VIEW=MATLABfig
COO=0.35        0.35        0.05
C2C=3.8613     -4.3644       1.671
ROO=0.596
ROLL=0
ORTHO=0.83893

PART=Mesh1
    RENDERMODE=SolidWireframe
END

PART=Mesh2
    RENDERMODE=SolidWireframe
END
END

The error disappears if I remove the 3Dviews options from one of them. But then I cannot configure the rendering of one model (transparency, light, etc).

I'm not familiar to the internals of latex, but looking at media9.sty it is clear that the command

\l_mix_vfile_stream

is used to open/close the .vws file.

Is this a bug from media9? or from latex 3?