Why is different the declaration class handle before and after the super call?

Hi, all

   //Case One

class BasePacket;
    int A;
endclass : BasePacket


class My_Packet extends BasePacket;
    int C;
endclass : My_Packet


class BaseTest;

BasePacket PB[string];

virtual function void Create_PKT(string s);
    PB[s] = new();
endfunction : Create_PKT

virtual function void Configure_PKT(string s);  
    PB[s].A = 1;
endfunction : Configure_PKT

virtual function void printP(string s);
    $display("BaseTest::PB[%s].A is %d", s, PB[s].A);
endfunction : printP

endclass : BaseTest


class My_Test extends BaseTest;

virtual function void Create_PKT(string s);
    My_Packet MP = new();
    PB[s] = MP;
endfunction : Create_PKT

virtual function void Configure_PKT(string s);
//  My_Packet mp;
    super.Configure_PKT(s);
    My_Packet mp;  
    $cast(mp, PB[s]);
    mp.C = 2;
    PB[s] = mp;
endfunction : Configure_PKT

virtual function void printP(string s);
//  My_Packet mp;  
    super.printP(s);
    My_Packet mp;
    $cast(mp, PB[s]);
    $display("My_test::PB[%s].C is %d", s, mp.C);
endfunction : printP

endclass : My_Test


BaseTest T1 = new();
My_Test T2 = new();

initial begin
      T1.Create_PKT("StringBase");
      T1.Configure_PKT("StringBase");
      T1.printP("StringBase");
      T2.Create_PKT("MY_String");
      T2.Configure_PKT("MY_String");
      T2.printP("MY_String");
end


//Output Information (Compiler Report Error)
//
//near "mp": syntax error, unexpected IDENTIFIER, expecting #





//Case Two

class BasePacket;
    int A;
endclass : BasePacket


class My_Packet extends BasePacket;
    int C;
endclass : My_Packet


class BaseTest;

BasePacket PB[string];

virtual function void Create_PKT(string s);
    PB[s] = new();
endfunction : Create_PKT

virtual function void Configure_PKT(string s);  
    PB[s].A = 1;
endfunction : Configure_PKT

virtual function void printP(string s);
    $display("BaseTest::PB[%s].A is %d", s, PB[s].A);
endfunction : printP

endclass : BaseTest


class My_Test extends BaseTest;

virtual function void Create_PKT(string s);
    My_Packet MP = new();
    PB[s] = MP;
endfunction : Create_PKT

virtual function void Configure_PKT(string s);
    My_Packet mp;
    super.Configure_PKT(s);
    //My_Packet mp;  
    $cast(mp, PB[s]);
    mp.C = 2;
    PB[s] = mp;
endfunction : Configure_PKT

virtual function void printP(string s);
    My_Packet mp;
    super.printP(s);
    //My_Packet mp;
    $cast(mp, PB[s]);
    $display("My_test::PB[%s].C is %d", s, mp.C);
endfunction : printP

endclass : My_Test


BaseTest T1 = new();
My_Test T2 = new();

initial begin
      T1.Create_PKT("StringBase");
      T1.Configure_PKT("StringBase");
      T1.printP("StringBase");
      T2.Create_PKT("MY_String");
      T2.Configure_PKT("MY_String");
      T2.printP("MY_String");
end


//Output Information
//
//# BaseTest::PB[StringBase].A is           1
//# BaseTest::PB[MY_String].A is           1
//# My_test::PB[MY_String].C is           2

  I designed two cases as above, ran case one, the simulator reported error as above.

  Would like to tell me the different of the declaration class handle before and after the super call?

  Thank you in advanced.

BR

QIN