Vertical page margin boxes are not insert/aligned correctly

Vertical page margin boxes are not insert/aligned correctly.

All three together work, but using only 1 or 2 fail

@page {
    @left-top {
        content: 'top';
        background: yellow;
    }
    @left-bottom {
        content: 'bottom';
        background: red;
    }
    @left-middle {
        content: 'middle';
        background: green;
    }
}