I worked on Google's CSS infrastructure for a while and there is a lot of logic that goes into what css rules get used where. You could be seeing that due to an experiment, a particular search result or a particular Version of Chrome. Google invests a lot of work in optimizing their css on the page with a lot of very complicated logic going into the choice of what rule to display and when.

Chrome on OS X here as well, mine does not get overwritten and stays as

     transform: scaleX(-1);

On both Firefox 37.0 and 41.0.2272.101 (gnu/linux x64, 3.19 yadda, yadda...)

    transform: rotateY(180deg);

is the cause of the change.

I'm curious which browser stringham is using.

I assume it forces the use of 3D composition.