invisible arrows using xypic have zero length

First, it is great that you've allowed the xypic package, thanks a lot for this!

The invisible arrow issue is not nearly as important as the fact that you've allowed producing xypic diagrams.

If this sort of question raises second thoughts about supporting xypic, then I'm withdrawing the question :) (seriously, though)

To the point, I have tried a couple of examples with invisible arrows, but all had the same problem (while producing the correct result when compiled in the usual way.