I can't believe this is something I read about only recently. It has probably been in the game since I started playing. I brought it up in guild conversation and about half the people knew, half didn't. So here is a topic to help inform even more people.
There is a way to undock health bars stuck together without having to close them all. Simply press Alt + Left-Click on the bar you want to move. Doing so releases it from the rest. The bar you clicked can now be dragged away or closed. If you press Alt + Control + Left-Click, you can drag the bar away without having to click a second time.
This is for the 2D client. I don't know if it works in Kingdom Reborn as well.
There is a way to undock health bars stuck together without having to close them all. Simply press Alt + Left-Click on the bar you want to move. Doing so releases it from the rest. The bar you clicked can now be dragged away or closed. If you press Alt + Control + Left-Click, you can drag the bar away without having to click a second time.
This is for the 2D client. I don't know if it works in Kingdom Reborn as well.