The one that had me puzzled, I don't remember which one it was, but I think Ichigo was back in the real world in the opening and there was this new girl. I don't know who she was, but it was really strange. It was like they were introducing a new love interest or main supporting character something. It was really strange. You probably know what I am talking about.
I'm pretty sure I know who you're referring to. That maybe a promo theme song to introduce the new Bleach Movie that has already come out in Japan but won't be here until for a very (very) long time. Hopefully you're talking about that girl who has purple hair that has been tied and she resembles Anko (from Naruto) quite a bit.

There was the one of the endings for like the fifth season I think where you see the Shinigamis dressed up in school uniforms. It seemed a little strange, seeing as I when they are their Shinigami forms they look older than school age. Some anyway. The captain of squad 10? I think, short white hair, H something, he fits, because he is short and looks like a kid still. But his vice-captain, she, err, looks too mature. Not to mention needs to button up.
That maybe the Bleach Sword Frenzy special. I remember that in the ending theme song (my computer soes not have sound anymore) that they slowly showed all of the Shinigami's in real life clothes? Well, Byakuya looked as if he were an aristocrat, noble, and he even had a long hat with a cane. o_O

I know they have this candy called Soul Candy that they use for their Gigai. For say when there is a hollow attack and they are in the real world, all they have to do is eat one of the sould candies and their Shinigmai souls come out of their bodies while a "replacement" soul takes their spot. There have been a few occurances where the souls may act strange and do things on their own.