the shading of the faces is all wierd afterwards, but when I delete the faces and fill mesh/bridge/apend polygon the shading is normal again.
Is this even an error with the model or just a displaying bug?
Here some screenshots for better understanding:
![user added image](https://abload.de/thumb/1bsu30.png)
![user added image](https://abload.de/thumb/2b5uoe.png)
-deleting the face closing the hole:
![user added image](https://abload.de/thumb/1akouk5.png)
this is how it looks before smoothing the marked edges are being smoothed maybe you have some tips and trick to get better results
![user added image](https://abload.de/thumb/3k3uhr.png)