I can't quite say for NDA reasons, but someone wrote a package, Package2, which attempted to provide all of Package1's functionality. They also added an extra subroutine, 'foobar', which could be exported. However, if something in your codebase loads Package2 and later you try to load Package1, it's already loaded and when it tries to export 'foobar', it blows up because it doesn't have it. The solution is to do a deep copy on the arrays. Otherwise, because Package2 has a reference to an array in Package1, modifying the array in Package2 modifies the same array in Package1. Does that make sense?

I know it sounds a bit convoluted, but there it is :)