A couple of points. On DBE controls, when you rotate through the squares, there are two arrow controls. One, with 1 arrow, moves you 1 square at a time. The double arrow jumps you 20. You must be using the double arrow by mistake.
As to nebulosity, you definitely do need to avoid the dust clouds, unless they are truly black. Otherwise you risk losing lots of detail in the subtle nebulosity. One way to avoid the problem is to do a maximum STF stretch so you can see the nebulosity more clearly so you can avoid it. Also, remember, you don't need many points for a good DBE solution unless you are dealing with serious light pollution gradients. I typically only place a couple in each corner and a few others dispersed around the rest of the image. More is definitely not better when using DBE.
Best,
Jim