Add component control disappears from region after dragging component

Problem/Motivation

After adding a component to a region, if you immediately drag that component into another region before saving, the control for adding a component to the original region disappears. If you drag that same component to a third region, the control re-appears on the first region but is missing from the second region.

Steps to reproduce

Add a section paragraph that has multiple regions (like a 3-column). Add a component to the first region, do not save. Drag the component to a second region. The plus button to add a component to the first region is gone.