When you complete Baldur's Gate 2 Shadows of Amn a final save game will be automatically created. Now when you start a new Throne of Bhaal game, you have the option to import that save game and just continue with your whole party.
After completing Icewind Dale this final save game is created too, but it serves no purpose at all. You cannot import it. All the characters you had in your party get automatically exported and you can import them into a new Heart of Winter game. But this is just cumbersome and non-intuitive. Furthermore all the containers like Bottomless Bag and their contents are gone, which just sucks!
It should just like it does in BG2. When importing the final save of the base game your group has all the equipment including containers. Most of the players that played BG2 probably expect this behaviour to be the same. I did and was very surprised finding out that it does not work like that.
I know that you can basically start the expansion from within the base game but it is strange to just move away from the main quest like that and also it would trivialize the final encounter of the base game.
It would be nice if this got changed.
PS: There is also a bug regarding that I'd like to report. The final save that is created after completing IWD is only created once. I deleted it and beat the boss afterwards again a few times. The final save has never been created again. The characters were not exported too. That means you have to do that manually too (I had to do it like that). It just is too cumbersome. It worked completely fine in BG2, it should work just as well in IWD.