can't define right associative extension method with type parameter

[bishabosha]

Compiler version

3.0.0-RC1

Minimized code

extension (s: String)
  def :*:[T <: Tuple](that: T) : String *: T = ???

Output

2 |  def :*:[T <: Tuple](that: T) : String *: T = ???
  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |  right-associative extension method must start with a single parameter

Expectation

no error