Menu items disappear

Hi,

I have a big menu on my site with around 150 items.

A few times items have disappeared from the menu when I update and save it.

What precisely happens is that I add a few items, update/save it and then when the page have reloaded I’m missing all the items from a specific point in the menu.

Like this:
– Menu looks like A-B-C-D
– Adding element E to menu, so it becomes A-B-C-D-E and update/save it.
– When the page reloads, it looks like this: A-B-C ??

1) Have anyone seen this before and know what to do about it?

2) Where are the menu items stored in the database, so I can backup the relevant table before I try to edit the menu again? (as it takes forever to add 50+ items back to the menu…)

Thanks,
Mads