Thank you Phiro and Michael.
.
>> external key remapping<<
The reason for my question is that I had remapped the zoom-function hotkey in
a way it was ergonomically perfectly close to all the other keys I mainly use.
Now it turned out that my new keyboard has difficulties in remapping the Ctrl -
key. Maybe I can find another workaround.

When the model is zoomed out, the lines on the back will be displayed, which is disordered. What is the reason?

Hi feirui445, that's the "bleed through" display artifact. Check out here for some more information:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4987.2

- Michael

Thanks again for your time.