The reference implementation of the Mersenne Twister was once GPL, although it wasn't anymore at that time. Still, there are only so many ways you can implement a Mersenne Twister. So my implementation got flagged.
Have you had a chance of trying out the report?
If you are scanning open source, there is a trick to ignore matches from the repository where it comes from.
Just create a file called "ignore.txt" inside the samples folder and on that file include the keywords that blacklist positive matches. For example, if scanning the "Adblock Plus" code then add as keyword "adblockplus" on the ignore.txt file and no matches from repositories containing "adblockplus" on their URL will be listed.
Works good for discovering which parts of an already open source project are not really original.