Getting code such as this:

class X
{
    public virtual void Test()
    {
    }
}

class Y : X
{
    public override void Test()
    {
        base.Test()   //added automatically, why?
    }
}

Because, by implication, that will not break anything.

Because in the majority of the cases it seems sensible or perhaps is even needed to call the bottom class implementation, e.g. virtual Dispose techniques (base class must be Disposed) or virtual OnXXX techniques in WinForms (base class usually fires a celebration using their OnXXX techniques).

Obviously when the virtual technique is yours and also you don't want this behavior To be sure it's pretty annoying )