Different sessions across controllers?

I’m seeing something odd or perhaps not, I really don’t know as I can’t
seem to find any information on this problem.

When accessing the various controlers in my application, I seem to get
different session objects, i.e., the object IDs are different. So, data
that I put into my session in controller A is not present when
controller B accesses the session (as it is a different object).
However, on subsequent requests through controller A, the session is the
same and my data is present.

Is there something special you have to do to maintain the same session
between application controllers? I’ve found tons of information on
shutting off the sessions on a per-controller basis, but nothing on
this. Any help is much appreciated.