I always thought that when you dropped a control onto an .aspx page that a declaration of that control ended up being generated for you (either in a designer file, or within your code behind). All of the apps I have worked on have worked this way.
A coworker of mine was installing resharper and it was showing that all her code behind pages would not build. Turned out that resharper could not find a definition for any control that she has dropped onto her markup. She has no designer files, and no declarations in markup. Do they get automatically built when putting together the partial classes? Is there an option at that page/project level to instruct .NET to do this for you? Is this a difference between web app and web site?

This is a a .NET 3.5 site, C#, and it is running in a production environment.

Thanks in advance