I did some more testing to make sure I was still getting the same results as last night...
That being said, it is still defaulting to append for me if no optional parameter is specified.
However, today when I tested, the optional parameter was working correctly when specified for both append and overwrite.
So I'll have to assume I was too tired and confused the parameters last night.
But, it's still defaulting to append, which is not a big deal in my opinion.
I could have sworn that it was overwriting when I used a 1 last night though.
EDIT: This was on Windows