That's intended behavior, controls group should not scale based on their contents. In many situations, you'll want it to remain static, while the content is scrollable (notable examples: diary text, field manual, functions viewer, welcome screen, etc.)
Since you are in control of its content, you can resize it manually (using https://community.bistudio.com/wiki/ctrlSetPosition), ideally applying some limits so it won't overflow outside of the screen.