Application verses and Bible section headings

I'm currnently working on Galatiasn 4:21-5:15.

I was struck how 5 verse 1 is as closely linked to what comes before as it is to what follows. If I were to preach only on the Sarah and Hagar story, I should rightly end with this verse. And yet in the NIV 5:1 is separated by a section heading.

How often does this happen? I know that 'therefore' marks a new logical entity, that it marks a new section. But it's sad the way Bible section headings do not form neat preaching units. Hebrews 1:1-2:4 is big another example.