hi osmium, Moynie, yes we notice those issues too. the problem is actually on browser side instead of on our code. this problem is because safari unable to understand RAF (request animation frame) perfectly.
we are using this RAF very extensively so we can get super smooth animation on chrome that implement RAF on their browser better than safari. on firefox also it work smoothly.
we will continue to look after safari development, and hopefully they will fix this issues.
ps: i think safari trying to safe as much as energy they have, so they sacrifice this feature.