On the odd occasion you wish to debug Seed method code which has been executed from the Package Manager Console using the Update-Database command, a quick and dirty method is to add the following code:
if (!System.Diagnostics.Debugger.IsAttached)
{
System.Diagnostics.Debugger.Launch();
}
Yes it's dirty! It will however fire up a new Visual Studio debug window and allow you to see what's going on inside.
This method will also work for any code that happens to sit outside of a normal debugging scenario.