[Xy-pic] bad positioning of an arrow tail

[Abdó Roig]

I have a problem with the positioning of an arrow tail using the
\xymatrix command in latex. The problem appears when I load the xypic
package and define the tail inside a custom package. I attach a couple
of examples.

The following code produces the expected result, an arrow of shape
>---->

File: test1.tex

  \documentclass[a4paper,11pt]{article}

  \usepackage[all]{xy}
  \newdir{ >}{{}*!/-10pt/@{>}}

  \begin{document}
    $$\xymatrix{A \ar@{ >->}[d]\\ B}$$
  \end{document}

But I want to include the \usepackage and \newdir commands inside a
custom package in order to avoid large preambles in my latex files. A
minimal example of this goes as follows:

File: testpkg.sty

  \ProvidesPackage{testpkg}
  \RequirePackage[all]{xy}
  \newdir{ >}{{}*!/-10pt/@{>}}


File test2.tex

  \documentclass[a4paper,11pt]{article}

  \usepackage{testpkg}

  \begin{document}
    $$\xymatrix{A \ar@{ >->}[d]\\ B}$$
  \end{document}

When I compile test2.tex the arrow tail is drawn shifted to the right
from the expected position.

Anyone has an idea of what is happening and how to solve it ?

Thank you very much.

Abdó.