Profile: Specified title in use

When adding profile fields, the title must be unique across all categories. Is this by design? I think it makes sense to only have titles unique within a category.

The following steps result in an error with the current profile.module:

1. go to admin/user/configure/profile
2. add single-line text-field: category: bar, title: foo
3. add single-line text-field: category: baz, title: foo
4. error: "The specified title is already in use."

The attached patch changes the behavior so titles only need to be unique in a category.