I don't do a lot of work with numbered lists, particularly multi-level, but I'm very sure that numbering cannot cross documents this way. I think, though, that for the second half document you can redefine the second level numbering to start at the correct number, rather than 1 or continue from previous.
Thanks Peter for your reply.
But why should it be possible to let the chapter number continue after a document cross, while the sub level number is not passed on the the next doc? If I am still in the same chapter, the sub level numbers continue.
And plus, what whould be the advantage of an automatic ( ! ) chapter numbering when the sub chapter numbering would have to be fixed manually?
To have either both or none would be logical, wouldn't it?
Where are you picking up the chapter number? My guess would be the number assigned as chapter number in the Numbering and Sections dialog, and that isn't necessarily sequenced automatically. You probably set it to be the same as the previous chapter in the book for that file.