umbraco/Umbraco-CMS — pull request #451 by AndyButland (2014-08-16 21:11:01+00:00)
Title: U4-5344 - Clear previous version after changing node document type

As per the related issue, it doesn't make much sense to keep previous versions and allow rollback if the document type as changed. Hence this PR which deletes the previous versions, and displays an on-screen warning indicating that this will occur.