SQLite Forum: Unexpected behaviour of the sum function

Due to a bug in our program we discovered an unexpected behaviour of the function sum().  
**We had the following scenario:**  

    CREATE TABLE "test" ("x"	REAL);
    INSERT INTO  test('1,2');
    INSERT INTO  test('1,5');
    SELECT SUM(x) FROM test

**Result:** 2.0  

I would expect an error message or a warning instead of a result pretending to be valid.