The shotgun sometimes appears to be shooting client-side after breaking a reload, but is not for strange reasons and when it happens you can see that it is still reloading.
I have tried to reproduce this on a client server in many ways, but I never successfully did it.
This happens quite often actually, on 3.0.4 and 3.0.5 servers. I notice that my client server is 3.0, so it might have something to do with the latest patches or it might just occur on servers not run by the client himself. Anyway.
As I said, this happens quite frequently and here is a demo taken from a 3.0.5 (first release, not the latest one) server. You can see myself shooting twice a skulk with a shotgun while none of the two shots registers. At the same time, you can see that the ammo clip is still reloading even though it appears to be shooting. My guess is that the shooting did not occur in third person, only client-side and that the reloading actually never stopped even if it should have.
shotgun.avi
Also note that most of the time the reloading can be stopped normally without this problem, so there seems to be something specific causing this.
Good luck