[Webkit-unassigned] [Bug 147284] New: incorrect position:fixed; rendering when child of position:relative; left:X%; element on OS X & iOS

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=147284

            Bug ID: 147284
           Summary: incorrect position:fixed; rendering when child of
                    position:relative;left:X%; element on OS X & iOS
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: webkit at rebertia.com

Created attachment 257494
  --> https://bugs.webkit.org/attachment.cgi?id=257494&action=review
Screenshot of incorrect Safari rendering

OS X Safari version: 8.0.7 (10600.7.12)
WebKit Nightly version: r186963
OS X version: Yosemite
iOS version: 8.4
Possibly related to: https://bugs.webkit.org/show_bug.cgi?id=122878
Original Bootstrap issue: https://github.com/twbs/bootstrap/issues/16814

It seems that WebKit/Safari places position:fixed elements incorrectly when they do not have a left/right/top/bottom property set on them and are a child of an element that is position:relative;left:X%;

See the attached screenshots. Safari renders the example differently from Chrome. IE11 and Firefox give the same result as Chrome.

To reproduce:
1. Open http://jsbin.com/rohemer in OS X Safari or iOS Safari.
2. Look at the red paragraph's text.

Actual result:
The red paragraph's text doesn't quite make sense, because part of it isn't visible.

Expected result:
The red paragraph's text makes sense because all of its text is visible.

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