How do I display the ~bounding box~ of a Render Border that is already created? A beginner's mistake, but it's driving me crazy. How do these bounding boxes work? Sometimes they appear, sometimes they do not. I can not figure out how to enable them in order to resize manually the Render Border that is already created.

How Render Border is usually:



How is it when the bounding box accidentally appears in the Render Border:



What is the trick? How do I display the bounding box?

Thank you.
I figured out. Simply select the active camera for the bounding box to appear. :D