Haxe - error, when trying to serialize object after cast to parent type

Question

I'm trying to do this:

var player:Player = new Player();  // class Player extends PlayerCore

var playerCore:PlayerCore = cast (player, PlayerCore);
var playerStr:String = Serializer.run(playerCore);

which compiles, but gives runtime error:

compile_server.command: line 3:  4267 Bus error: 10           ../bin/Server/Main

Cast works, it fails on serializer line. Except that Std.is(playerCore, PlayerCore) and Std.is(playerCore, Player) are both true, I don't know if it is expected result or not. Is this Haxe / hxcpp bug or am I doing something wrong?

Or alternatively, I need to convert object of type Player to it's parent type PlayerCore ("strip it off" the Player type features) and then serialize it. Is there a way to do this properly, or do I need to create new object and copy all the parameters manually?

Haxe 3.2.1, hxcpp 3.2.180, mac target