Typescript Visitor Pattern missing type info

I seem to be losing type info using the visitor design pattern in typescript:

abstract class AbsVisitor
{
  public abstract visitPerson(p: Person): void;
  public abstract visitAddress(p: Address): void;
}

class StrVisitor extends AbsVisitor
{
  public visitPerson(p: Person): void {
    console.log(`XXX ${typeof p}  XXX`) // <--- type Person is lost !
    console.log(`name: ${p.name}`);
  }
  public visitAddress(a: Address): void {
    console.log(`XXX ${typeof a}  XXX`) // <--- type Address is lost !
    console.log(`{a.street}( ${a.num} )`);
  }
}

class Person {
  constructor(public name: string){}
  public accept(v: AbsVisitor){ v.visitPerson(this); }
}

class Address {
  constructor(public street: string, public num: number){}
  public accept(v: AbsVisitor){ v.visitAddress(this); }
}

let v = new StrVisitor();
let p = new Person("moish");
let a = new Address("5th Ave.", 62);
p.accept(v);
a.accept(v);

When I run it, I get the sub-optimal (incorrect?) result:

XXX object  XXX
name: moish
XXX object  XXX
{a.street}( 62 )