The menu is not correct, either. There are two commands available: “Play from Start of Flow” (Option+Shift+Spacebar, as @dankreider said) and “Play from Start of Project” (I use German localization). Both do the same, though, and play from the Beginning of the first flow/Start of Project, as far as I can see.
The commands are found directly in the Play menu, not in a separate sub menu called “Start or Stop Playback” like @dspreadbury described; maybe that’s the only difference of the development build’s GUI here.
Until this feature is corrected, you might use the keycommand “Set playback mark to begin of flow” (default Num,), which works as expected and hit space afterwards.