It might be a bug that the icon isn't reflecting the state of the parallel pool properly. Nevertheless, I'm assuming you can run a parfor/spmd over the pool?
Keep in mind, if you call parpool('local'), you're getting the default number of workers to start up, just as if parfor started for you the first time. So in essence, you don't need to add this to startup. MATLAB will start it when you need it. You only need to explicitly call parpool if you don't want the default parameters (e.g., profile, number of workers, etc.).