Discrepancies with elixirc and mix compile

It’s come up a few times recently how the following code snippets are equivalent when compiled:

def Foo do
  def foo do
    String.capitalize("foo")
  end
end

and

def Foo do
  import String

  def foo do
    capitalize("foo")
  end
end

I’m not questioning how this works or anything, I understand the latter essentially gets rewritten to the former. However, when compiling each with elixirc, the resulting binaries are not only different but one is a slightly larger than the other (we’re only talking a few bytes here). But when put into a mix project and compiled with mix compile, the binaries are the same size, but still differ (no difference if compiled in dev or prod or as a release). I’m assuming this is just the @vsn attribute, but clearly I don’t actually know.

What gives?

EDIT: If this is even a valid test, I manually set @vsn and they still differed in mix.