Derivation fails when record update is used as a data index

[buzden]

Consider the following example:

record X where
  constructor MkX
  field : Nat

data Y : X -> Type where
  Start : Y r
  Next : Y ({field $= S} r) -> Y r

genY : Fuel -> (x : X) -> Gen MaybeEmpty $ Y x
genY = deriveGen

I'd expect this derivation to succeed, but it fails with

While processing right hand side of genY.
Error during reflection:
While processing right hand side of $resolved13352,<Deriving.DepTyCheck.Gen.Y>[0].
While processing right hand side of $resolved13352,<Deriving.DepTyCheck.Gen.Y>[0],<<Deriving.DepTyCheck.Gen.Next>>.
Deriving.DepTyCheck.Gen.case block in $resolved13323 is not accessible in this context.

I suspect coding of field update syntax through some case block does this, maybe we need to workaround it somehow on the library side.