position:fixed-related rendering bug on iPad Pro in Landscape orientation

Number:rdar://24030853 Date Originated:01-Jan-2016
Status:Open Resolved:
Product:Safari Product Version:iOS 9.2
Classification:Other Bug Reproducible:Always
Descendants of a position:fixed element are sometimes rendered incorrectly (with a rectangular chunk clipped out of them and replaced with whiteness) in Safari on an iPad Pro when the device is in Landscape orientation.

Steps to Reproduce:
1. Get an iPad Pro (or open the Xcode Simulator for iPad Pro).
2. Rotate the device (or use the "Rotate Right" in the Simulator) so that it is in a landscape orientation.
3. Open https://output.jsbin.com/sicula/1 in Safari
4. If using the simulator, ensure that the virtual device has actually remained in a landscape orientation.
     (Opening Safari appears to reset the orientation to Portrait in some circumstances.)
5. Tap the green "Setup" link on the webpage.
6. Observe that a menu is displayed below the link.
7. Tap the cyan "Tools" link on the webpage.

Expected Results:
A menu should be properly displayed below the "Tools" link, like it was for the "Setup" link.

Actual Results:
The menu displayed below the "Tools" link is missing a rectangular chunk on its left side.
See attached screenshot and GIF video.

iOS 9.2

WebKit bug: https://bugs.webkit.org/show_bug.cgi?id=152637
Original Bootstrap bug report: https://github.com/twbs/bootstrap/issues/18738

This bug only occurs on iPad Pro and not on other iPad models.
This bug only occurs when the iPad Pro is in Landscape orientation, not when in Portrait orientation.
This bug only occurs when the navbar is styled as `position: fixed`.
This bug is visually very similar to (and thus presumably related to) https://bugs.webkit.org/show_bug.cgi?id=138162 , although that bug involves zooming and applies to a wider range of iOS hardware models.

iPad Pro, in landscape orientation

'ipadprorepro.gif' and 'screenshot.png' were successfully uploaded.


Please note: Reports posted here will not necessarily be seen by Apple. All problems should be submitted at bugreport.apple.com before they are posted here. Please only post information for Radars that you have filed yourself, and please do not include Apple confidential information in your posts. Thank you!