When the window containing a layout is invisible, the layout's dimensions will not update when contents change. This is especially noticeable when a window is sized by its contents, as it will flash to the size with no contents before updating to the size it wants if the platform allows.

The bug can be easily reproduced with the attached sample as shown in the video. Add elements and print the dimensions before the window is visible, then do it again while visible. Notice the dimensions only update while the window is visible.