instance brackets right of the colon in meta definitions

Stream: general

[Chris Hughes]

This code makes an error, but works if I make the instance brackets into explicit brackets, or remove the meta. Is this a bug?

meta def f : Π {α : Type} [h : decidable_eq α], nat := sorry

[Kenny Lau]

another reason to prefer the better implicit brackets:

meta def f : Π ⦃α : Type⦄ [h : decidable_eq α], nat := sorry

[Yury G. Kudryashov]

But there is no next explicit argument