Runtime error with dynamics in default definitions

Hi, I'm getting a runtime error when trying to use dynamics in default definitions:

class test a where
  test :: a -> a | TC a
  test y =
    case (dynamic y) of
      (y :: a^) = y

instance test Int, Bool

Error:

Bring up to date...
Compiling...
Analyzing 'main'.
[main.icl,]: no abc file
Compiling 'main'.
Run time error, rule '<case>[line:2591];15;746' in module 'type' does not match
read failed 0

I would expect this to work, or at least give a clear error of some sort.

Edit: Environment: iTasks with -aui compiler flag