Django South removes foreign key REFERENCES from SQLite3 schema. Why? Is it a problem?

When using syncdb the following schema is created:

CREATE TABLE "MyApp_supervisor" (
    "id" integer NOT NULL PRI开发者_JAVA百科MARY KEY,
    "supervisor_id" integer NOT NULL REFERENCES "MyApp_employee" ("id"),
    "section_id" integer NOT NULL REFERENCES "MyApp_section" ("id")
);

When using migrate, it is changed to:

CREATE TABLE "MyApp_supervisor" (
    "id" integer NOT NULL PRIMARY KEY,
    "supervisor_id" integer NOT NULL,
    "section_id" integer NOT NULL
);

Why does South do that? I haven't noticed a functional problem yet, but I'm weary of ignoring this...

Can someone shed some light on what is happening here?

---

It's probably because foreign key support was introduced in SQLite only in version 3.6.19, as this page says:

This document describes the support for SQL foreign key constraints introduced in SQLite version 3.6.19.

It looks like version 3.6.19 was tagged on 14th Oct 2009, which is actually quite recent so it's probably not deployed everywhere yet.

I guess the choice was made not to declare foreign keys because they're not widely supported yet, depending on the version of SQLite used. (This being said, the foreign key syntax was supported before, but simply ignored.)