The standard keyboard shortcut for switching the keyboard layout is Command-
Space, but the Mac driver never sees the Space key press. So, Wine only sees
a press and release of Alt, which puts focus on the menu bar. This prevents
that focus change.
It's fairly common in Mac keyboard layouts that, if you type a dead key twice,
the second key press will both produce a non-dead character and also
perpetuate the dead-key state. For example, with the U.S. layout, Option-E,
E will produce "é" and Option-E, Option-E, E will produce "´é". Windows
keyboard layouts don't tend to do this. The second key press produces the
non-dead character and clears the dead-key state.