The following TextEdit will render the underline through the text instead of under it (note that there is an asian character followed by some latin characters):

TextEdit {
    text: "\u6277 abc"
    font.family: "Noto Sans CJK SC"
    font.underline: true
}

Tested with Noto Sans as well as Droid Sans fallback. The problem doesn't occur with typefaces lacking east asian characters. The problem doesn't occur with TextInput, either.