User blog comment:Kirkburn/Technical Update: March 3, 2015/@comment-1045255-20150305110638/@comment-4738639-20150305123717

I actually prefer it on the right because of the same reasons because the "Preview" button was aesthetically closer to where that box is than the mobile box.

I may be remembering incorrectly though, but I am used to clicking more towards the right for preview.