The attached test case demonstrates this. The buttons update the justify/alignment properties of the flex container, but the items are not repositioned correctly. Toggling off the original style set on the flex contain (via the inspector) works. It appears a repaint is happening. I'm on 536.5 (@118056)
Created attachment 145875 [details] Test case
I don't have time to investigate this right now, but I suspect that the bug is that in RenderStyle::diff, we don't compare the new values on rareNonInheritedData. Previously, we would compare rareNonInheritedData->m_flexibleBox against each other, but moving the values to rareNonInheritedData doesn't automatically do this. Once we realize that the style has changed, we'll probably re-layout properly. The fix is probably around line RenderStyle.cpp:376.
Created attachment 145903 [details] Patch
I wasn't making progress on my other bug, so I decided to fix this :)
Comment on attachment 145903 [details] Patch Clearing flags on attachment: 145903 Committed r119564: <http://trac.webkit.org/changeset/119564>
All reviewed patches have been landed. Closing bug.