baernty on "Nav Menu Limit"

Every time I add a new nav menu item, WordPress deletes the last item in the nav menu. I currently have around 90 menu items. Below this limit everything works fine.

I think the problem is a "suhosin" PHP Plugin on my Webserver.
Does anyone know which variable to increase?

Is there a workaround for wordpress to use other variables in the nav-menu admin screen which will not be limited by some plugins?

Thanks very much!