Why is scalafmt gluing these lines together?

Question

I have this type definition:

type Foo = Bar
   with Baz
   with Bat
   with Bak
   with Bar

Which I like formatted the way it is. But even with newlines.source=keep scalafmt glues them all into one line (and what's even worse, breaks it into too lines if it ends up being longer than maxColumn):

type Foo = Bar with Baz with Bat with Bak
  with Bar

... which, to me, looks completely unreadable :(

Why is it doing this, and is there a setting that would make it preserve my formatting?

Update In response to comments, here is the entire script:

[sandbox] [1123]> cat .scalafmt.conf
version = "3.7.16"
runner.dialect = scala213
newlines.source=keep
maxColumn = 40
[sandbox] [1124]> scalafmt --version
scalafmt 3.7.16
[sandbox] [1125]> scalafmt --test foobar.scala 
--- a/Users/dima/sandbox/foobar.scala
+++ b/Users/dima/sandbox/foobar.scala
@@ -1,9 +1,4 @@
 class Foo {
-  type It = Foo with
-    Bar with
-    Baz with
-    Bat with
-    Bak with
-    Bam with
-    Ban
+  type It = Foo with Bar with Baz
+    with Bat with Bak with Bam with Ban
 }
error: --test failed