In the old days of SharePoint 2007, the master page reference in a publishing page layout lived in the MasterPageFile attribute of the @Page reference at the top off the layout file.
This made good when you needed to create a page layout that stood out from the common branding of the site – such as a page layout that had no chrome for popups etc… and this was exactly what I wanted to accomplish today in SharePoint 2010.
Unfortunately, Microsoft changed the way in which Page Layouts associate with their master page. Open any of the out of the box page layouts in SP2010 and you should notice that there are no references to master page files anywhere. This is because the master page association is handled by the containing site settings.
So how does one go about creating a “special” page layout that does not follow the same branding as the rest of the site? One option is to isolate such pages in sub sites, which is frankly crappy. Unfortunately, the alternative is much better – the general consensus is that the solution to this problem consists of creating a new sub class that inherits the PublishingLayoutPage class and sets the CustomMasterUrl property explicitly in the Page Init event.
Thanks to Eric for his post, which I referenced to solve this issue.