UICollectionView fails to honour zPosition and zIndex - iOS 11 only

Originator:foundry.tv
Number:rdar://34308893 Date Originated:7 September 2017
Status:Open Resolved:
Product:ios + SDK Product Version:ios 11
Classification: Reproducible:Yes
 
Area:
UIKit

Summary: Zindex and ZPosition are not honoured in CollectionView headers


Steps to Reproduce:
Set up a collectionView with a header and cells. Set the zPosition or zIndex of the header to position it below the level of the cells. 


Expected Results:
Header is positioned below the level of the cells

Actual Results:
Header is positioned above the level of the cells, as if the zIndex or zPosition had not been changed

Workaround:
Add a small delay before setting the zPosition (0.35s seems to work)

Version/Build:
This only occurs on iOS11 and only if building with XCode 9
Tested on XCode 9 beta 5 and XCode 9 beta 6. 
Simulator (SE and 6 tested) and Device (SE / ios11 beta).

Comments

it seems fixed in iOS 11.1

update: building with XCode 9 GM and running on ios11 GM exhibits the same bug


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