Then, only last Friday, I was helping out a guy who is relatively new to SharePoint branding and development etc. and had been trying out this and that in VisualStudio to help him get along - and avot! He had found the solution to the problem. Maybe it is old stuff to you already, but it was a life-saver for me!
In the Solution Explorer, right-click on the MasterPage/PageLayout file missing intellisense, select View Markup. That does it, pals!