Summary: animation of transform does not work with with spring() timing function. When there is a spring it appears to be linear. However, animating a transform does work with other timing functions (e.g. ease-in, ease-out). Compare: <http://codepen.io/joepeck/pen/JKOpPj/> - animate left with spring() => spring! <http://codepen.io/joepeck/pen/AXbVBz/> - animate transform with spring() => linear
I thought we explicitly turned off spring in animations, while we work out what it means. The fact it works for left is a bug :)