OnMouseOver GUI flickering if mouse moves Y

Hey Community.

I have a strange "flickering-problem" with GUI-elements. I've build a small c# script for collectable items. If the mouse hovers over an object a gui appears with some infos. It works so far, but if you move the mouse in Y the GUI is flickering. Did not find something to fix that in forum/answers...

Here's the code: using UnityEngine; using System.Collections;

 public class MakeItem : MonoBehaviour {
 
     // Definition
     public string name; // Name of that THING
     public string description; // Tell something about it
     public float weight = 1; // WTF is it so heavy? in kg
     public int slotType; // Where to put this shit (1=Backpack, 2=Toolbelt, 3=?)
     public int slotSize = 1; // Damn this takes a lot of place
     public int use = 1; // Can I use it? Throw it? Put it in my hand?
     public int stackSize = 1; // Stack it if you want, bro
     public float spawnrate; // Limit the spawnrate to INFINITE ;)    
     public int condition = 100; // good, weak? in percent
     public Texture2D icon;    
     
     private bool showItemInfos = false;
     
     void OnMouseOver() {
         showItemInfos = true;
     }
     
     void OnMouseExit() {
         showItemInfos = false;
     }
     
     void OnGUI() {
         if(showItemInfos) {
             int y;
             // get mouse position
             Vector3 mousePosition = Input.mousePosition;        
             
             // Draw some infos
             GUI.Box(new Rect(mousePosition.x,Screen.height- mousePosition.y, 100, 100), description);
             //print ("X: " + mousePosition.x + " Y: " + mousePosition.y);
             
             // show item infos
             GUI.BeginGroup(new Rect(Screen.width - 210, 10, 200, 200));
                 // draw a box as border
                 GUI.Box(new Rect(0, 0, 200, 200), name);
                 y = 20;
                 GUI.DrawTexture(new Rect(5, y, 50, 50), icon);
                 y += 50;
                 GUI.Label(new Rect(5, y, 200, 20), "Description: " + description);
                 y += 20;
                 GUI.Label(new Rect(5, y, 200, 20), "Weight: " + weight);
                 y += 20;
                 GUI.Label(new Rect(5, y, 200, 20), "Condition: " + weight);
             GUI.EndGroup();
             //print ("X: " + transform.position.x + " Y: " + transform.position.y);
             //GUI.Label(Rect(mousePosition.x, mousePosition.y), name);
         }
     }
 }