[Xy-pic] arc overshooting endpoint

[Leslie Saper]

Hello,

The following code produces two diagrams.  The first connects the origin
to point at <10pc,4pc> by a circular arc beginning with an angle of 45
degrees.  The output is as expected.  The code for the second diagram is
identical except the point is 1 pica higher.  But in the output the arc
overshoots the point by around 3/4 inches.

\documentclass{article}
\usepackage[arc,pdf]{xy}
\begin{document}

\xy
*\dir{*}
;+<10pc,4pc>*\dir{*}
,{\ellipse ru,_{}}
\endxy

\xy
*\dir{*}
;+<10pc,5pc>*\dir{*}
,{\ellipse ru,_{}}
\endxy

\end{document}

What did I do wrong?  Or is this to be expected and why?

I am using Xy-pic version 3.8.4 processed with pdflatex.  The output pdf
file may be found at

https://www.math.duke.edu/faculty/saper/arc_test.pdf

Thanks,

Leslie Saper