We have been having a problem with the turnitin plugin with moodle 1.9 and with moodle 2.x consisting of the plugin processing files that are not accepted as valid type by turnitin. This causes lots of confusion for students seeing the errors and cannot be avoided by creating multiple assignments for each file type. A simple example is a programming assignment which has a zip containing coded and a word doc for the assessment piece. The solution I have provided a patch for, simply uses the turnitin "valid file list" as a default config parameter and will not process any invalid files into the turnitin files table. This seems to work effectively and has not caused any errors since.