Hm, yes, I agree, that seems a bit random.
Do you restore the course with user data or without? What happens if you copy/restore without user data?
Also, I think there's a setting in the Turnitin plugin that allows it to be used in assignments, forums etc (that's plugin configuration setting in site administration). Maybe you could switch off its use for forums? I'd also check if Turnitin is off by default (that's also in the plugin configs).