GUI.tooltip is not set when hovering dynamic created buttons

Like many other people before and after me i'm working on a RPG inventory and i got some problems with getting a tooltip when hovering over the different Items.

Everything works fine but the tooltip...

I tried nearly any of the ideas i found in unityAnswers and inside some unity community forums.

I'm coding in c# so for now i use a new GUIContent(string, string) to set the tooltip and yes, that works perfectly on few buttons i specified exactly, each by its own rect and throws it out on Debug, boxes, labels aso.

But in my inventory i don't want to define every single button so i'm using a for loop running through lines and rows, creating all buttons. I guess somehow the tooltip information is not set or changes to fast to be shown inside this loop.

Anyone got any other idea on how to get this done?

     /// <summary>
     /// Dos the bag window.
     /// </summary>
     /// <param name='_id'>
     /// _id.
     /// </param>
     void DoBagWindow (int _id) {
         int _fieldCount = 0;
         string _itemDescr = string.Empty;
         Rect _fieldRect = new Rect(0,0,0,0);
         Texture2D _tempTex = _defaultTexture;
         
         BaseItem _tempItem = null;
         
         if(GUI.Button(new Rect(_screenHeight-25, 5, 20,20), "X", healthtext)){
             _selectedWindow = 100;
         }        
         GUI.BeginGroup(new Rect(10, 10, 300, 300), string.Empty);
 
         for(int _lines = 0; _lines < 7; _lines++){
             for(int _rows = 0; _rows < 7; _rows++){
                 _fieldCount++;
                 _fieldRect = new Rect(_rows*40, 10+_lines*40, 40, 40);
                 if(_inventory.INVENTORYSIZE > _fieldCount){
                     _tempItem = _inventory.GetItemAtSlot(_fieldCount);
                     
                     if(_tempItem != null){
                         _tempTex = _tempItem.APPEARENCE;
                         _itemDescr = _tempItem.DESCRIPTION;
                     }
                     else{
                         _tempTex = _defaultTexture;
                     }
                 }
                 if(GUI.Button(_fieldRect, new GUIContent(_tempTex, _itemDescr))){
                     if(_tempItem != null)
                         Debug.Log("Clicked " + _tempItem.NAME);
                     else
                         Debug.Log("Clicked an empty Slot");
                 }
             }
         }
         GUI.EndGroup();        
     }