Affinity isn't working and clients connections are balanced??

We have an ASP.NET application that updates (every 3 seconds) and it seems
that "Single Affinity setting" isn't keeping a user connected to the same
session on a server - instead the http request is getting redirected to the
server in the cluster.

We have 2 servers in the cluster - and all of the clients will connect to
the server with 1st priority (not load balanced). If I "stop" 1st server (in
NLBMgr), all clients are directed to the other server (which is expected).
When I "start" the 1st server (in NLBMgr), the clients seem to randomly swith
from the 2nd server to the 1st server several times, and finally will connect
to the 1st server.

Why isn't the affinity setting keeping the user connected to the same
session and why aren't the client connections being "balanced" across both
servers?

--

-Kevin