Not sure what's causing it - might be on my end - but when I check the 'Quote' box on posts and use the 'Quote Checked' function in the Quick Reply field at the bottom of a thread, it creates double quotes. I shall demonstrate in the post below.
This is with Chrome version 36.0.1985.125 m, by the way.
Edited, Jul 28th 2014 1:40am by Mazra