loop GUI Buttons doesn`t respond

Why my GUI buttons created in loop doesn`t react if clicked? Only first button respond.

 void OnGUI(){
     if(show_inventory){
         inventory_window_rect = GUI.Window(inventory_window_id, inventory_window_rect,     inventory_func, "INVENTORY");
     }
 }
             
 void inventory_func(int id){
     inv_counter = 0;
     putted_in_inventory = false;
     for(int i = 0; i< 6; i++){
         for(int j = 0;j < 4; j++){    
             inv_counter++;
             item_name = "";
             if(inv[inv_counter] == 0 && (weapons_behaviour.equiped || shields_behaviour.equiped) && !putted_in_inventory){
             
                 if(weapons_behaviour.just_equiped){ 
                     item_name = weapons_behaviour.weapon_name; 
                     weapons_behaviour.just_equiped = false;
                 }
                 if(shields_behaviour.just_equiped){ 
                     item_name = shields_behaviour.shield_name; 
                     shields_behaviour.just_equiped = false;
                 }
                 unique = true;
                 
                 for(int l = 0;l<=24;l++){
                     if(item_name == items_names[l]) unique = false;
                 }
                 
                 if(unique){
                 
                 inv[inv_counter] = 1;
                 items_names[inv_counter] = item_name;
             }
             }
     >>>>>>>>>>>>>>>>>>**These buttons doesn`t respond!**<<<<<<<<<<<<<<,<
     if(GUI.Button(new Rect(5+(j * 40), 20 + (i*40), 40, 40), items_names[inv_counter])){
             items_names[inv_counter] = "";
             inv[inv_counter] = 0;
             Debug.Log("Button clicked");
     }
     GUI.DragWindow();        
 }
 }
 }