There exists a page "Foo" in a space called "Space 1."
If I choose to copy (by clicking Copy) that page to "Space 2," the system suggests a name "Copy of Foo" (or similar, all's fine so far.)
While still in the edit mode, I change the title back to "Foo" and choose a destination space of "Space 2" and click save, the system reports that "There already exists a page "Foo" in space "Space 1"" (or similar.) Which is kinda silly as I'm not creating that page to Space 1, but to Space 2.
To make this work I need to first create the copy, and then rename it to "Foo."
Not a biggy, but seriously annoying as it misleads innocent users.