Hello noderaser,
While I can't say why you are getting a new host ID so often, and not having an example of such a "split", I would say that is probably an anomaly caused by BOINCstats retrieving data from different projects at different times. If you look at the duplicate entries through BOINCstats, see if either of the duplicates has a project in common; I'll bet that they don't. If they are disappearing after a few days, it's because BOINCstats has received the updated information from the projects and recognizes the new host CPID for all of the projects.
I see you found my original thread.
Here is an example.
And here is another one.
You are right in that the split host are split exactly along projects, and one by one the projects are moved to the newest host.
But this has never happened before with any update of BOINC, and it has happened on every host that I updated to 6.10.56/.58.
It also is not restricted to BOINCstats, as you can see from the two links above.
In addition, you find the very same effect every time I hook up the host to a different network (home, hotel, friend). The respective host immediately branches of a new ID, which over time collects all the projects again. Until I hook it up to a different (or the old) network, causing it to split again.
What is most annoying is the fact that it is impossible to really get any idea of a hosts performance because it is split into 2 or even three IDs. And since all the projects are migrated to the latest host ID, I always loose my history (like "Best 5 days"

.
So the fact that
- this never happened with any host at any BOINC update before,
- this happened to every host I updated to 6.10.56/.58 exactly the moment I updated it,
- this happens again every time I switch networks, and
- this is not restricted to BOINCstats
make me believe, this is a BOINC bug.

But as I said, if it is something I can fix, please let me know about it.
I would be extremely delighted if this would stop!
Friedrich