import QtQuick
import Qt5Compat.GraphicalEffects

Window {
    id: root
    width: 400
    height: 300
    visible: true

    Canvas {
        id: btn
        width: 100
        height: 50
        anchors.centerIn: parent
        onPaint: getContext("2d").fillRect(0, 0, btn.width, btn.height)
    }

    // Moving this MouseArea into the Canvas causes the problem to disappear
    MouseArea {
        id: mouseArea
        anchors.fill: btn
    }

    DropShadow {
        anchors.fill: btn
        source: btn
        radius: mouseArea.pressed ? 0 : 3
        transparentBorder: true
        verticalOffset: 3
        horizontalOffset: 3
    }
}