Re: Issue with rectangle mouse selection

[Mattias Engdegård]

> Terminal.app and Gnome Terminal are fine, but Xterm exhibits the behaviour 
> you describe.

XTerm does indeed not report mouse movements when modifiers are used, so there 
is little Emacs can do about it.
This may be intended; the source (button.c) contains

    /*
     * We reserve shift modifier for cut/paste operations.  In principle we
     * can pass through control and meta modifiers, but in practice, the
     * popup menu uses control, and the window manager is likely to use meta,
     * so those events are not delivered to SendMousePosition.
     */

If this bothers you, perhaps you could ask the maintainer to reconsider; 
gnome-terminal manages, after all. (XTerm clearly needs more options. Just like 
Emacs.)