Steps to reproduce:
1. Apply 'Extension Method to Plain Static' refactoring through SC popup menu to following code:

static class MyExtClass
{
    public static void Ext{caret}(this IMyClass z)
    {
        z.Foo();
    }
}
internal interface IMyClass
{
    void Foo();
}
class MyClass : IMyClass
{
    public void Foo()
    {
    }
}

2. See text in the list of Undo button in the Standard toolbar.
Wrong result: text is 'VS Command', but it should be something like 'Extension Method to Plain Static'.