Open Radar

 
Summary:
The modal presentation stack can end up in the wrong order after adapting to a different presentation style when a custom presentation controller is involved in the modal presentation stack.

Steps to Reproduce:
Follow these steps using an iPad that supports spit view.

1) Present a modal view controller with a custom presentation controller
2) Present a modal view controller with a modal presentation style of `UIModalPresentationFormSheet` (no custom presentation controller needed)
3) Present a modal view controller (no custom presentation controller needed)
4) Adapt to/from full screen to force the form sheet to adapt presentation styles

Expected Results:
I expect the view controllers to still be presented in order. The visible order should be:

1) custom presentation controller
2) form sheet
3) standard view controller

Actual Results:
The visible order is wrong. It is:

1) custom presentation controller
2) standard view controller
3) form sheet

This can leave the application in an unrecoverable state.

Version:
iOS 9.2

Notes:
This appears to happen with any standard adaptivity. For example, using a popover instead of a form sheet causes the exact same issue.

Configuration:
iPad Air 2 (device or simulator)

Attachments:
'sad-modal.zip' and 'sad-modal.mov' were successfully uploaded.