There is a known issue with the Joomla! 1.5.7 upgrade regarding the way articles are ordered in Front Page Blog Layout. If you upgrade an existing site to 1.5.7, and if you have two or more columns, the Front Page Layout will default to ordering articles down the columns instead of across the columns.
To fix this, all you need to do is
This will initialize the default parameter and cause the articles to be ordered across columns as before.
This bug was a side effect of a new feature that allows you to have Section Blog, Category Blog, and Front Page layouts order either down or across columns. Note that this issue will also affect the Joomla! Sample website in a new 1.5.7 installation. New sites are not affected by this issue.