rfl produces error: unknown declaration 'Bool.false'

Stream: lean4

[Tomas Skrivan]

Playing around with reduceBool revealed this odd error with rfl tactic:

def a : Bool := false
example : false = Lean.reduceBool a := by unfold a; rfl

It produces (kernel) unknown declaration 'Bool.false' error which looks suspicious. The nat version

def b : Nat := 42
example : 42 = Lean.reduceNat b := by unfold b; rfl

fails with the expected error

tactic 'rfl' failed, equality lhs
  42
is not definitionally equal to rhs
  Lean.reduceNat 42

What is going wrong? Is this a bug with rfl tactic?