Subject: bug#26104: 26.0.50; In Ubuntu, having mouse over other frame cause Alt key to produce a <switch-frame> event

From: martin rudalics <[email-masked]>
Date: Fri, 17 Mar 2017 08:19:56 +0100

> In Ubuntu, if I have two frames open and the mouse is positioned over the other frame (i.e. not over the active one), pressing the Alt key produces a <switch-frame> event.
 >
 > While this event does nothing in itself, it disrupts things like yank-pop, which no longer works if it is bound to M-y as usual (because instead of the command sequence yank -> yank-pop, we now have yank -> handle-switch-frame -> yank-pop, which gives an error "user-error: Previous command was not a yank").
 >
 > To be honest, I don't know enough about X-Windows to know if this is emacs' fault or x-windows fault. But it's very annoying.
 >
 > [Tried on Emacs versions 24.5, 25.1, and the 26.0 and Ubuntu 16.10.]

Could you try in simple.el to replace

   (if (not (eq last-command 'yank))
       (user-error "Previous command was not a yank"))

with

   (if (not (memq last-command '(yank handle-switch-frame)))
       (user-error "Previous command was not a yank"))

Thanks, martin