ZEOSLIB increasing memory usage inside TThread

I tried to run a SELECT SQL to retrieve some data from MySql database. For this, I had created a TZQuery inside a TThreadn to avoid freezing the GUI of the application.

But, after the end of each consult (tested with 100,000+ rows, just to "force" a freeze) the memory was increasing instead of returning to the initial values (even after FreeAndNil(ZQuery) and FreeAndNil(TThread)) increasing ~2mb to each query executed (verified using Windows taskman.)

The test:

1 - Click button1 to start thread and query

2 - Wait callback

3 - Click button2 to finish and free query

    { TForm }
    
    procedure TForm1.Button1Click(Sender: TObject);
    begin
      //DBQuery: TSubThreadTest;
      DBQuery:= TSubThreadTest.Create(SQLStatement, true, ZCon, @onQueryCallBack);
      DBQuery.Start;
    end;
    
    procedure TForm1.Button2Click(Sender: TObject);
    begin
      FreeAndNil(DBQuery);
    end;
    
    procedure TForm1.onQueryCallBack(fail: boolean; query: TZQuery);
    begin
      lLastExec.Caption:= FormatDateTime('hh:mm:ss', Now);
    end;   
    
    { TSubThreadTest }
    
    constructor TSubThreadTest.Create(SQLStatement: string; toExec: boolean;
      connector: TZConnection; EOnConclude: TSubThreadTestCallBack);
    begin
      inherited Create(true);
    
      //main: TZQuery;
    
      main:= TZQuery.Create(nil);
      main.Connection:= connector;
      main.SQL.Text:= SQLStatement;
    
      isToExec:= toExec;
    
      OnConclude:= EOnConclude;
    
      FreeOnTerminate:= False;
    end;
    
    
    procedure TSubThreadTest.callback;
    begin
      if assigned(OnConclude) then
        OnConclude(true, main);
    end;
    
    procedure TSubThreadTest.Execute;
    begin
      if isToExec then
        main.ExecSQL
      else
        main.Open;
    
      Synchronize(@callback);
    
      FreeAndNil(main);
    end;

First thread create and call: 24mb memory usage

Second thread create and call: 26,5mb memory usage

Etc...