Haxe 4.2.x regression

When upgrading some code from Haxe 4.1.5 to 4.2.x, I found the following regression:

```haxe

abstract MapProxy(Dynamic) {

@:from static inline function fromMap(map:Map):MapProxy {
return null;
}

}

class Test {
public static function main():Void {
var m : MapProxy = new Map();
}
}
```

This used to compile fine but is now failing with:
```
Test.hx:12: characters 3-44 : haxe.ds.Map : Int & EnumValue & String & Int & String & EnumValue & { }, Unknown<1>> should be MapProxy
```