Steps to Reproduce
Set Slate.EnableGlobalInvalidation=1 for the project.
Have an SExpandableArea in some UI (use UExpandableArea if needed) that contains some widgets in the Body.
Run PIE with “in a new window” option (or run a cooked build). Important because the Editor window doesn respect globalinvalidation in the same way.
Toggle the expandable area expansion.
Observe that the Body contents appear and disappear, but the size occupied by the expandable area, does not change.
Expected the area occupied by Expandable Area to change.
You can also then run `Slate.TriggerInvalidate` in the console and see the area update.