Open Radar

 
When a subview of a NSSplitView configured with auto layout is collapsed, this wrongfully also affects other subviews of the split view.
Instead of expanding their sizes accordingly to the space that was set free by the collapsed view they slightly change position and reveal their underlying view. This causes an ugly visual glitch demonstrated by the attached demo project and screen shots at http://imgur.com/jHLADIh

This is a regression and doesn't occur in OS X 10.9 or 10.10 as can be verified by running the demo on those versions.

Steps to Reproduce:
1. Build and run the attached demo project
2. Collapse the blue subview by dragging its divider to the left

Expected Results:
The blue subview should be collapsed while not affecting the other subviews or dividers.
It should look like shown in success.png (OS X 10.9, 10.10)

Actual Results:
The blue subview is collapsed but also caused a change to the second divider and thus to the size of the purple view. The underlying view (colored yellow) leaks.
It looks like shown in failure.png (OS X 10.11)

Version:
Xcode 7.0 beta (7A121l)
OS X 10.11 (15A204h)