My extreme hills edge and extreme hills have both a large smooth radius and use volatility1 and volatility2. When they generate next to each other (which very frequently happens as EHedge is the border of EH) there are often giant cliffs like in the image. I think that shouldn't happen as the smooth radius of both is high. Weird things also happen when EH (or a different biome with vola1) generates next to one without that setting turned on.
More information can be found in the image.

After some PM's back and forth this is being converted to a Feature Request for the ability to set a flag that would include Volatility1 and Volatility 2 in the smoothing process. Those two settings currently do not get smoothed out.

Using the instructions and images I PM'ed to @Timethor this is reproduceable.

(I accidentally closed it. It's reopened now. I hope so actually :D

Any plans of adding this feature? Most of the biomes I use uses volatility 1 and 2 and it would be nice if i could smoothen the edge of biomes.

After much investigation, this seems rather unfeasible without more effort than I am prepared to give at the moment. This issue will remain open but I have no plans of implementing it anytime soon. Maybe in a rewrite?

@Timethor
Can't you just do something like this?

-- Current process of world generation --
Generate terrain
Use smooth radius
Add vola1 and vola 2
Add other stuff

Isn't that changeable to this?

-- Some other kind of process that could possibly solve this issue --
Generate terrain
Use smooth radius
Add other stuff

@Timethor
Can't you just do something like this?

-- Current process of world generation --
Generate terrain
Use smooth radius
Add vola1 and vola 2
Add other stuff

Isn't that changeable to this?

-- Some other kind of process that could possibly solve this issue --
Generate terrain
Add vola1 and vola 2
Use smooth radius
Add other stuff

(As you know, I can't code, so I don't know how difficult this is to change.)

Or do you have a workaround? @Timethor

@Timethor (now I see you're online ;) ) there are sometimes weird things happening with biome intersections with and without vola1/2. Sometimes giant cliffs or walls or floating stuff generate when two of those biomes meet, creating weird terrain that shouldn't generate in those biomes.
I created a 2D image explaining what's happening sometimes in the terrain.
There are two biomes, green (G) and blue (B).
G doesn't use vola1/2, B does.
If B didn't use vola1/2, it would generate like light blue. You can see it generates in this example mountainous terrain with floating islands, so the green biome gets a bit of that mountainous terrain at the edge, because of smoothradius.
But B does use vola1/2, and because of this settings, the terrain is randomly a lot lower at that point than it would be without. But as smoothing happens before vola1/2, the smoothing creates a lot of mountains and weird stuff at the edge of G, assuming B generates weird and high. So you get G with a mountainous edge. Then in the generating process, vola1/2 is used, so you get the lower terrain in B (darker blue). And suddenly there's a big wall and floating island in the sky because of an incorrect smoothing process!

You understand what's happening, right? (If my explanation wasn't clear, that might have happened, please say that, I'll try to explain it better then) The smoothing process creates this weird terrain that in this case shouldn't happen. And of course the opposite may happen too.