Created attachment 185051 [details] test case I've only been able to reproduce this with content_shell on Linux. I tried Chrome on Linux and Chrome/Safari on Mac with no luck. If I load this page on startup of content_shell (i.e. pass the path to the page on the commandline), the animation consistently does not run. I think this is exposing a genuine non-content_shell race condition, but it's hard to be sure if there's just something weird content_shell is doing. Stumbled across this looking at the reduced test case on https://code.google.com/p/chromium/issues/detail?id=160638. Not sure if this is affecting any real sites.
I modified -webkit-transition value from .5s to 60s and ran "chrome file:///tmp/testcase.html". I saw transition animation. I think, if it takes a little much time for chrome to load some page which has css transition, the transition would be finished. So we cannot see any transition. Since I'm not familiar with css transition spec, I'm not sure whether this behavior is valid or not.
Going to assume this was Chromium only given we've never heard anything since.