The patch adjusts the sidebar's panels size when region overlap is active, in order to remove the blank space between them and the tabs bar introduced by the recent visual update of the panels.

When region overlay is on it basically restores the previous look (except for the vertical distancing, which remains) while keeping current master behaviour everywhere else.

I hope to have understood properly the implication of those "no header" panels but I'm a bit rusty here :)
To test them I temporarily added region overlap to the graph editor, and the F-curve modifiers one looked correct to me.