Adding Bundling and Minification to a Sitecore project

We added ASP.NET bundling and minification to a Sitecore 6.5 project (webforms, using .NET Framework 4) You can read an introduction on bundling and minification here: http://weblogs.asp.net/scottgu/archive/2011/11/27/new-bundling-and-minification-support-asp-net-4-5-series.aspx After setting everything up we noticed a very unreliable behavior, sometimes the bundling worked sometimes we got an ItemNotFound exception from Sitecore. So then we found this post: