incrediBILL - 7:22 am on Jul 31, 2012 (gmt 0)
I already explained what it is.
Not that I don't agree with your explanation, I couldn't find anything that definitively claimed it was the problem and I found others claiming my explanation.
I've got a couple of high traffic sites and a bunch of new sites and I've never seen this "undefined" stuff on any of my sites, ever.
Doesn't mean I dispute it happens but I'd sure like to find a specific reproducible case study to definitively be able to state the cause.