[Xy-pic] Revisiting alignment problems

[Michael Abbott]

Following earlier discussion on the topic of entry alignment I have taken
to adding the following line to my macro file with largely good results:
	\entrymodifiers={+!!<0pt,\fontdimen22\textfont2>}
However, I have encountered a quirk that I can't see a solution to; can
anyone else explain what's happening here?

	\documentclass{article}
	\usepackage[all]{xy}
	\begin{document}
	Compare
	\xymatrix{
	 & \ar@{-}'[d][dd] \\
	\ar@{-}[rr] & & \\
	 &
	}
	with
	\entrymodifiers={+!!<0pt,\fontdimen22\textfont2>}
	\xymatrix{
	 & \ar@{-}'[d][dd] \\
	\ar@{-}[rr] & & \\
	 &
	}
	\end{document}

Here we have two identical diagrams showing one line crossing over
another, with the under-crossing line drawn as \ar'[d][dd].  Unfortunately
the \entrmodifiers statement seems to have displaced the hole in the line
so that the second diagram comes out wrong: the hole is no longer
centrally aligned with the over-crossing line.

Is there a workaround?