Hi,
I've just updated my computer to AE CC 2014 running on OS X Yosemite, and I've been searching around but can't find anything on this subject.
When I do a RAM preview of my work area, it won't start playing from the beginning. It loads the whole working area, and if I have sound/music I can hear the music start playing from the beginning, but I won't see the image playing until after ~1 second.
It's not due to the RAM preview "From current time" setting, that's turned off.
Specs:
MPB Retina Late 2013
2,3 GHz i7
16GB RAM
GeForce GT 750M 2048MB
OS X Yosemite
After Effects CC 2014