Bug with multiple Scanner objects?

I had a couple freshmen submit code that multiple scanner objects created and used when only one was needed. They were able to run the code fine locally, but failed test cases. Deleting superfluous scanner objects seemed to fix things. I was just wondering if this was a known issue or some isolated incident I should check more closely. It's hard to search the forums but I didn't find anything there or in the bug tracker for 'scanner'.