Inheritor of openstruct is deserealized to it's base struct

I have the following model:
```kotlin
object BuildModel: Ext(IdeRoot) {
val buildEventModel = openstruct {
field("id", string)
field("message", string)
}

val startBuildEventModel = structdef extends buildEventModel {
field("buildDescriptor", buildDescriptorModel)
}

val buildDescriptorModel = structdef {
field("id", string)
field("title", string)
field("workingDir", string)
field("startTime", long)
}

init {
signal("buildEvent", buildEventModel).async
}
}
```

I push a `StartBuildEventModel` to the signal from one side and I get a `BuildEventModel` on the other side.