dotted identifier notation error

Stream: lean4

[Yuri de Wit]

Consider the following example:

inductive Term
| cell

inductive Equation (α: Type := Term)
| act (l: α) (r: α)

def test1 : List Equation → List Equation
| .act c c1 :: eqns => []
| [] => []

def test0 : List (Equation RuleTerm) → List (Equation RuleTerm)
| .act c c1 :: eqns => []
| [] => []

Here, test0 and test1 work as expected.

However, the following example does not work:

inductive RuleTerm
| cell

abbrev RuleEquation := Equation RuleTerm

def test2 : List RuleEquation → List RuleEquation
| .act c c1 :: eqns => [] -- ERROR! invalid dotted identifier notation, unknown identifier `RuleEquation.act` from expected type RuleEquation
| [] => []

Fixing this is easy: use Equation.act instead of .act. However, should this be considered a bug or as-designed?