See screenshots for an example.

Can be reproduced easily on any monitor by going into windowed mode and making the screen a little less wide.

The effect is only seen in a certain range of aspect ratios.
Once you go into a more square-like shape, however, everything becomes smaller to fit the screen.

Probably because size is caclulated by the size of the two buttons at the bottom instead of the widest component (the scrollable area).

The contents of the scrollable area is also a little off-center on the controls screen. It could be moved a little more to the right (to center it). There is no need for a margin to the right of the scroll bar.