> Magical incantations! ;-) I positioned it and then used `xinput
 > disable ID` for both my mouse and trackpad.

And what would make you that sure that the `handle-switch-frame' event
was not inserted before you disabled xinput?

Anyway, as a first attempt try to apply the attached patch to keyboard.c
and tell me what the value of the variable `lispy-switch-frame-source'
is when you try your M-y.

martin