Load the following file:

data A : Set where
  bad  : A
  very : A → A

pattern good = very bad

-- {-# DISPLAY very bad = good #-}

data P : A → Set where

data Q : A → Set where
  cons : ∀ {q} → P q → Q q

Wrap : Set
Wrap = Q good

x : Wrap
x = cons {! !}

y : Q (very bad)
y = ?

Agda 2.8.0 displays:

Visible Goals:
?0 : (P (very bad))
?1 : Q good

I would expect something closer to what happens if I un-comment the explicit DISPLAY pragma:

Visible Goals:
?0 : (P good)
?1 : Q good

[there's also the question of P good getting parenthesized for no particular reason, but that one is less pressing]

This is especially puzzling considering that the documentation for pattern synonyms states:

For each pattern pattern lhs = rhs, Agda declares a DISPLAY pragma refolding rhs to lhs (see The DISPLAY pragma for more details).