See the following demo: http://codepen.io/SitePoint/pen/VLXQmM Notice in all other browsers, the ball stops halfway. In Safari, the ball stops briefly, then jumps to the end. This seems to be an attempt to apply the "forwards" value of the fill mode. But this is incorrect behaviour. The "forwards" state is at the half-iteration point, not the full iteration. Sorry for not creating a RTC. Someone could easily do that using the code in the demo, if necessary. Note also that the demo is using autoprefixer to add the missing "-webkit" prefixes automatically, so these don't actually appear in the CSS panel.
Nice find, thanks!
<rdar://problem/21886103>
Created attachment 257042 [details] Patch
Comment on attachment 257042 [details] Patch Attachment 257042 [details] did not pass mac-ews (mac): Output: http://webkit-queues.appspot.com/results/5700661509357568 New failing tests: animations/fill-mode-iteration-count-non-integer.html
Created attachment 257044 [details] Archive of layout-test-results from ews100 for mac-mavericks The attached test failures were seen while running run-webkit-tests on the mac-ews. Bot: ews100 Port: mac-mavericks Platform: Mac OS X 10.9.5
Comment on attachment 257042 [details] Patch Attachment 257042 [details] did not pass mac-wk2-ews (mac-wk2): Output: http://webkit-queues.appspot.com/results/6454754687320064 New failing tests: animations/fill-mode-iteration-count-non-integer.html
Created attachment 257045 [details] Archive of layout-test-results from ews106 for mac-mavericks-wk2 The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews. Bot: ews106 Port: mac-mavericks-wk2 Platform: Mac OS X 10.9.5
Created attachment 257047 [details] Patch
Comment on attachment 257047 [details] Patch Clearing flags on attachment: 257047 Committed r187121: <http://trac.webkit.org/changeset/187121>
All reviewed patches have been landed. Closing bug.