this.type strangeness

Hi, all:

===
class A {
def b(): this.type = {
val r = this
r
}
}
===

Fails to compile: found : r.type (with underlying type A) required:
A.this.type. Is it a bug, or I don't understand how this.type work?

I know workaround:

===
class A {
def b(): this.type = {
val r: this.type = this
r
}
}
===

S.