Wrong items distribution on UIToolbar

Number:rdar://6468254638 Date Originated:20/03/2018
Status:Open Resolved:NO
Product:UIKit Product Version:
Classification:bug Reproducible:YES
When adding the same instance of UIBarButtonItem initialized with an image several times to a UIToolbar along with some flexibleSpace between them, it doesn't seem to distribute the items properly. However if you add different instances of UIBarButtonItem or the same instance but initialized with a title, it works perfectly. 
The results for both iOS 8.0 and iOS9/iOS10/iOS11 are different since on iOS9 and newer the UIToolbar uses a UIStackView internally to distribute the items.

It is quiet unlikely that a developer want to add the same instance of UIBarButtonItem to a UIToolbar, but It could be the case. In case that it won't be fixed, It would be necessary to update the documentation to clarify it.

Steps to Reproduce:
- Create UIToolbar.
- Create UIBarButtonItem and name it as "item" for instance, with the init(image:style:target:action) initializer 
- Create UIBarButtonItem (flexibleSpace system type) and name it as "flexibleSpace" for instance. 
- Set the items to the UIToolbar like so: setItems([item, flexibleSpace, item, flexibleSpace, item], animated: true)


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