What Don said is correct. What stainless are you using? The 300 series (austenitic) are much more resistant to rust than the 400 series materials (ferritic).

Some times there is iron in the grinding wheel or media that gets trapped in the surface and causes 'rust'. When ground the fresh material is exposed to oxygen and will re-passivate naturally. However if there was foreign matter such as iron on the surface it can become trapped and will rust. Keep it clean and you should be OK. Make sure there is no iron oxide in any buffing compound you may be using etc.

Kitz