Same query, same filter yields different results:
15 hits - http://localhost:8080/?q=%22Microsoft.Office.Interop.Excel%22&lan=MSBuild%20scripts
0 hits - http://localhost:8080/html?q=%22Microsoft.Office.Interop.Excel%22&lan=MSBuild%20scripts

I noticed that in even result address gets different, maybe related to space in language name:
http://localhost:8080/?q=%22Microsoft.Office.Interop.Excel%22&lan=MSBuild%20scripts
http://localhost:8080/html/?q=%22Microsoft.Office.Interop.Excel%22&lan=MSBuild+scripts