I struggle with t forgetting stuff some too, although my t probably hasn't gone as far as your t. I haven't been talking to my t very long, so it's hard to tell.

As far as the t saying we'll talk about something in the next session, I've had 2 t's now who say that and don't do it. After a while with the first one, I asked her if she remembered what we talked about the last time. She said "very well" and gave me a lot of detail about what we had talked about! I was surprised she really did remember. Now I think that she was suggesting something possible to talk about in the next session, more as a way to end the session than as a direction to actually talk about it. She was not very directive at all; she would wait for me to come up with topics to talk about. That wasn't working for me and I quit. Later, with another t, I came to like bringing up the topics more sometimes. Now my current t sometimes says "I want you to think about blah blah blah" at the end of a session. Now that I realize he's not going to bring it up again, I don't expect it so it hasn't bothered me (yet). I'm getting the impression t's tend toward being scattered and forgetful, although your t is going too far with that.

I guess an advantage of not staying focused on a topic is it's more likely that what you talk about will be spontaneous and natural instead of something we clients already thought about a lot. On the other hand, too much lack of continuity sucks... especially when t's forget really important things!