It's not play/play/pause.
It's initiate preview / quit rendering frames to RAM and give me full speed playback of what you have renderered / pause
More details (including info on how to change this behavior) here: all about previews in After Effects CC 2015 (13.5) | After Effects region of interest
Thanks Szalam, but why does it play while it's "initiating preview"? It means that when I do say "quit rendering frames to RAM and give me full speed playback of what you have renderered" it just carries on from wherever the playhead has reached rather than showing me a RAM preview from where I set the playhead initially.
From the article you linked I think I need to choose Preview favours Length rather than Preview favours Frame rate.
It plays while it's initiating a preview so you can see the frames as they render instead of waiting. This is not dissimilar to how RAM Preview used to work. I found this to be very beneficial. I don't want to wait for it to render 20 seconds worth of stuff if I notice something awry in the first two.
Lots can be adjusted. Read the page I linked.
I agree, it's great to see what's happening while it's loading those frames. I did read that article before I started this thread but this parameter is not adjustable. It will initiate the preview from the playhead or the start of the timeline, but the second time play is hit just plays from where it has loaded frames up to, rather than jumping back to the beginning. I would like to see a realtime preview from the playhead in order to time action to audio. I guess it will just take some getting used to.
I think a lot of the preview issues I am having are around timing to audio. The images load fine but audio playback is all over the place. I hear they are planning on fixing these bugs in July.