Created attachment 446039 [details]
Steps to reproduce:
I have attached a screencast of this:
1. Go to https://codepen.io/emattias/pen/NWaxYrp?editors=0110
2. Press "toggle start animation button"
3. See the leftmost column animate in without a problem
4. Press "css transition on" button
5. Press "toggle start animation button" again
I can reproduce this in the latest firefox and safari versions but not in chrome. I think the way chrome handles it (not applying css transition) is what I prefer and expect to happen (since the width has not changed).
Have you also filed a bug on Chromium? I haven't looked into whether Chromium was right and Firefox+Safari was wrong, but given they are the only engine with a different implementation, it would be good to get their take on this as well.
I created a chromium bug for this here: https://bugs.chromium.org/p/chromium/issues/detail?id=1279736