Hi Carlo,
I tried zooming in 3 different operational views with 3 different maps and it happens on all of them.
I have also tried it on 3 different computers, it happened there as well.
Here are 2 images of what happens. If you look at the area, which I have marked with a red rectangle, you can see symbols disappearing and one is even showing only half.
[ATTACH=CONFIG]22731[/ATTACH]
[ATTACH=CONFIG]22732[/ATTACH]