TabButton implicitWidth Strange Behaviour (in TabBar)

[Puya]

Hi. How come in this code the implicitWidth of TabBar changes when I comment out width: implicitWidth in TabButtons? (I am trying to create a vertical TabBar) Why does the fact that I am setting width of a component to be its implicitWidth (which I assumed was the default behavior anyway when width is not set) change the implicitWidth? You can run this example with qmlscene:

import QtQuick 2.15
import QtQuick.Controls 2.15
import QtQuick.Layouts 1.15

Item {
   id: root
   height: 480
   width: 640

   RowLayout {
      anchors.fill: parent

      TabBar {
         id: bar
         Layout.fillHeight: true
         implicitWidth: Math.max(homeTabButton.implicitWidth, discoverTabButton.implicitWidth, activityTabButton.implicitWidth)

         background: Rectangle {
            color: "yellow"
         }

         contentItem: ListView {
            // orientation: ListView.Horizontal
            model: bar.contentModel
         }


         TabButton {
            id: homeTabButton
            width: implicitWidth
            text: qsTr("Home")
         }
         TabButton {
            id: discoverTabButton
            width: implicitWidth
            text: qsTr("Discover")
         }
         TabButton {
            id: activityTabButton
            width: implicitWidth
            text: qsTr("Activity")
         }
      }

      StackLayout {
         Layout.fillWidth: true
         Layout.fillHeight: true
         currentIndex: bar.currentIndex
         Pane {
            id: homeTab
            background: Rectangle {
               color: "blue"
            }
         }
         Pane {
            id: discoverTab
            background: Rectangle {
               color: "red"
            }
         }
         Pane {
            id: activityTab
            background: Rectangle {
               color: "green"
            }
         }
      }
   }
}

[Puya]

I have created a SO question as well in case someone wants to answer there instead:
https://stackoverflow.com/questions/64267727/qml-why-does-tabbars-implicitwidth-depend-on-binding-inner-tabbuttons-width/64330266