We upgraded our Joomla sites from 3.4.8 to 3.6.5 a while ago and it looks like the default behavior on how the alias for Menu Item Type [Menu Item Alias] is generated has changed. And this is either a bug or a deliberate change as others are also having this issue
On 3.4.8, when I create a Menu Item Alias for 'Page 1' with a alias/slug 'page-1', it would simply autogenerate a timestamp as the alias.
On 3.6.5, if I create a Menu Item Alias for menu item 'Page 1', it tries to create an alias 'page-1', which is already used by the menu item I am creating an alias to and hence it throws a duplicate alias error.
Is this change documented anywhere so that I can see the reasoning behind it? Or is this a bug?