Can't save changes in Appearance → Menus after rearranging menu

[rbag]

Can't save changes in Appearance → Menus after rearranging menu.

Wordpress version: 3.5

Number of menu items: 24

Procedure to reproduce:
Add 5 pages as top menu pages, then add 5 pages under each page (see my site ​http://bildr.no/view/1342664). Click Save. Then rearrange pages and save again. You will now see a blank page. Reload page and you will see that your changes are lost/no rearrangement took place.

Bug related: #22189

I tried to increase timeout on server without solving the issue (will try to increase timeout later even more when webmaster is back and then report back the result).

[Ipstenu]

Duplicate of #14134.