Untill the current version of blogger, the URL* matched the title of the post. That meant, that each time you modified the the title, the URL changed. Perhaps this caused a series of 404 errors for spiders and RSS readers and they decide to fix it by giving a unique URL* for each post that maches the first written title.

What means that for the ones that want a litlle SEO spice in their blogger blog:

Now you can create a post with your target keywords in title, publish it and then return and change the title to a more human friendly format. Before doing that play around to detect what are the maximum characters allowed in the URL.

*When I say custom URL I am reffering to the part that comes after blogspot.com/