How to show list & thumbnail widget in plupload?
The Plupload integration module does not support the UI components of the Plupload Library. It is just as the module name suggest an integration with the library. The actual preview/thumbnails of uploaded images is handled by other modules like in your case FileField Sources Plupload and FileField Sources. You can check the module maintainers answer here. For modules that integrate with Plupload scroll down to the list on the module page.