I dont know if this problem is common or not but i came to know about this problem today.
It seems that after a certain amount of menus have been added to the menu it suddenly stops adding any more to them.
In my case i was not able to add any extra menus items after 85th one.
It seems the server times out or something...but it does not seem fair to those who use a shared server to make chnages to the server setting each time this problem appears...
So guys at wordpress please fix this problem as soon as possible as i am a fan of wordpress and also i dont want this problem to continue..