"Effect is not allowed in this context" caused by effect with type argument of boxed effectful function

```effekt
interface Foo {}
interface Bar[C] {}

def a(): Unit / Bar[() => Unit / Foo at {}] = ()

def b(): Unit / {} = {
try a() // Effect Bar[() => Unit / { Foo } at {}] is not allowed in this context.
with Bar[() => Unit / Foo at {}] {}
}
```
The issue disappears if `/ Foo` is deleted.