[Agda] Ill shaped metavariable?

[Ondrej Rypacek]

Hi all,
is this normal:

Goal: _≡_ {IdObj G n} (⟦_⟧Obj {G} {n} x) (⟦_⟧Obj {G} {n} x')
Have: _≡_ {IdObj G n} (⟦_⟧Obj {G} {n} x) (⟦_⟧Obj {G} {n} x')

I.e. I have what is asked of me, but yet the goal wouldn't be accepted
? With an error which an error which doesn't make sense to me, and
I've tripple-checked everything, so am really puzzled.

The source is a bit complicated to be posted here, so I wanted to
check whether this is possible at all (and if there are some likely
causes) before trying to come up with a simpler example.

Cheers,
Ondrej