Looking at maps of Päijänne Tavastia I noticed, near Enonvesi lake in Heinola, that there's a small enclave of Päijänne Tavastia inside Southern Savonia.
The smaller area is just touching the main part of Päijänne Tavastia, but don't seem to overlap.
Why is this? And how did this come about?
I've searched to see if there's anything particularly historic or special about Enonvesi, but didn't find anything. I also checked the satellite photos but they didn't reveal much other than trees and a few small roads to lakeside buildings.
The only place name Google Maps shows inside this smaller area is Mäntyranta, which doesn't reveal much.
I found an Internet site, that contains some knowledge about the history of the Enonvesi-region and it's villages, http://www.enonkylat.fi/historiikki/. As far as I understand, part of the area has belonged to the cultural region of Häme from early on, the fiscal authorities and the nearest church have been in Häme. That could probably be the explanation to the fact that thist part, called Paadenmaa, still belongs to Päijät-Häme and not to South-Savonia.
There is a contactform on the pages of Enonkylät ry, they could possibly give you more accurate information, http://www.enonkylat.fi/?f=1.