Does accessing UI controls inside ComDataPacket.OnPacket needs thread synchronization?

Question

I have a ComPort1 and a ComDataPacket1 on my form and ComDataPacket1.ComPort:= ComPort1;. I see that there is a properties SyncMethod and I guess that TComPort creating a thread when ComPort1.Connected:=true;.

Recently I realized that every UI access from OnExecute event of Indy IdTCPServer component needs to be Synchronized with MainThread so is it true for TComPort? How to do this(Indy has a class to doing this)?

I am reading data from com port like this(data is sent as packet so ComDataPacket1 is very useful):

procedure TForm2.ComDataPacket1Packet(Sender: TObject; const Str: string);
begin
    Label1.caption:= str;
end;

I am working on a project and sometimes I got famous "Your application has stopped working" message box(When my program is closed). I am suspecting this error is because of that.