I deleted the email, but from what I remember the problem is:
@argv = "123456"
split("4", at argv)
The context forces @argv to a scalar, much like $n = @argv.
So the @argv tranlsates to 1.
A more convincing example is:
@argv = ("123456") x 123
split("2", at argv)
results in 1,3
It is the result of the count of the elements being split.
Peter