I was messing with using a second preview window because I wanted to see if the second window would stay maximized when switching between nodes, like Objects->Renderers (where the preview window re-sizes to the smaller size when changing nodes.) I like to maximize the preview especially when doing population edits. I found it didn't change from maximized, which is great.
Then I got to wondering about the pause button. Is it separate (as far as the function of pausing or not) from the pause button on the other preview window? At first I thought it was, since both buttons toggle (on my system clicking cause the button to go to a lite blue when in pause. However, I found that they (pause buttons) can get "out of sync" as shown in the image below.