Blog weirdness

I had a blogpost "Christmas" which seemed to have disappeared. It did not show up in my blog archive list, but searching for "Christmas" turned up the post, so where did it go. I changed the blog archive box to use a flat layout, which looked like this:

In the blog archive list there are now 2 (!) entries for March:
http://thisisnotaprogrammersblog.blogspot.com/2009_03_01_archive.html, and http://thisisnotaprogrammersblog.blogspot.com/2009_03_31_archive.html.

Can anyone enlighten me about what's going on?