Composed key events not captured in qwebengine

When switching my keyboard layout to "Swiss German" on macOS I can compose ä by typing "a .

When I try to capture the keydown events with javascript:

document.body.onkeydown = function(e){console.log(e.keyCode + " : " + e.key);};

I receive, when I type h"ase, only

"72 : h"
"83 : s"
"69 : e"

The composed ä is missing from the keydown events.

On Chrome I receive

72 : h
229 : Dead
229 : ä
83 : s
69 : e

I attached a sample project qwebengine_compose.zip which is logging the js keydown events.