We tag production releases with svn. In Hudson we do have a project for each project, that is configured on a svn repository location which is updated to the most current production branch by using svn externals (svn propedit svn:externals .).
I made a tag that ended with the current date (...20100330), but when I updated the external definition I set that one to
....20100329, a tag that does not exist at all. When you update svn on that tag, svn fails - but hudson did not report any failing update, instead it
rebuild the entire project, using the files it had checked out the last time. This resulted in a bug fix release without any real fixes on the client site.