It depends on the grade of the stainless steel. Different alloys have different chromium, nickel, and other metal contents. Hard (martensitic) stainless grades (like 400 series stainless steels used in cutlery) have less chromium than the soft 18Cr-8Ni grades that are used for most anti-rust applications. Also, some alloys have lower chromium content to lower cost. It is my guess that the Kahr is made with a lower chromium (cheaper) grade of martensitic stainless.
It also depends on your personal body chemistry, some people have more problems with rust on a weapon kept close to the body than others. The problem is definitely not unheard of.
You can probably use a light abrasive to remove the rust, but you will likely be unable to match the finish on the rest of the gun; I have not handled a Kahr in stainless, so I don't know whether it is a bead blasted or polished finish, but you will not be able to match the original without polishing or bead blasting. Perhaps someone else can suggest another rust removal method. Nick19