Some flickering occurs when having IMGUIContainers in the scrollview. This is caused by the fact that now the layout of scrollview is performed in multiple frames but also the fact that the size of IMGUIContainer changes inexplicably each frame. The latter issue is likely caused by the fact that IMGUIContainer computes the layout of the wrapped IMGUI control during the Repaint pass instead of the Layout pass

Steps:

1 - Create a document

2 - Select the Root item in the Hierarchy pane

3 - Resize the UI Builder window to squeeze the inspector to a really small height to display the Scrollbars

4 - Enlarge the UI Builder window bit by bit a couple of times

Actual outcome:

The flickering happens or the vertical scrollbar remains visible without the thumb.