Pop-up windows are not ordered properly when using VisualElement.add() method

Reproduction steps:

1. Open the attached project “UITKbug“
2. Go to “Window > App UI > Open Storybook”
3. In the window “App UI - StoryBook” open “Kit > Main”
4. Scroll down till you reach the “MENU” section
5. Press the button “Click here!”
6. Select the list item “My Sub Menu > Another Sub Menu > Another Sub Menu Item”

Expected result: Pop-up windows stack on top of each other
Actual result: The order of pop-up windows is reversed

Reproducible with: 2021.3.15f1, 2022.1.0a16
Not reproducible with: 2022.1.0b1, 2022.1.24f1, 2022.2.0f1, 2023.1.0a22
Couldn't test with: 2020.3.42f1 (Packages/com.unity.dt.app-ui/PackageResources/Styles/Themes/App UI - Globals.tss (line 8): error: Unsupported unit: '200ms')
Fixed in: 2022.1.0b1

Reproducible on: Windows 11

Note: If any script is modified in any way, then after saving the script the order of Sub Menu items is fixed