I am a self-taught Muslim. It is my understanding that the number of rakahs in Sunnah prayer (any Sunnah prayer) should be 2. If you want to pray 4, then you break it up (2 + 2). Even in taraweeh, we break it up into pairs.
But I have been observing people praying 4 rakahs continuously and giving salam in their 4th rakah (like in the sunnah prayer before Zuhr and Asar). Is this also acceptable?