foo.{$u} is not supported

[Vtec234]

For consistency, I would expect that when we have u : Level then inside q we could use $u to refer to it. This seems to work sometimes, whereas at other times we need u inside q. The inconsistency is confusing. For example:

open Lean Qq
example (u : Level) (T : Q(Sort u)) (t : Q($T)) := q(@id.{$u} $T $t) -- unknown universe level '«$u»'
example (u : Level) (T : Q(Sort $u)) (t : Q($T)) := q(@id.{$u} $T $t) -- unknown universe level '«$u»'
example (u : Level) (T : Q(Sort u)) (t : Q($T)) := q(@id.{u} $T $t) -- works
example (u : Level) (T : Q(Sort $u)) (t : Q($T)) := q(@id.{u} $T $t) -- works?!