In M4, when I click "View Line Numbers" from an XSLT stylesheet, a dialog
box pops up that will never go away indicating there's no Listener method
attached to the current window (I'm not phrasing it exactly, but I can get
the exact error message if you need it). The only recourse is to kill the
Designer process. Has this been identified by anyone?

This was an upgrade from 1.x to 2.0 M4.