I found this:

http://blogs.psychcentral.com/alway...udent-make-these-careless-math-mistakes/

I think we are definitely looking at the first issue (student is under pressure). We could consider this a good thing! DD has found math easy for 5.5 years of school, up till right about now! She is finally hitting some challenge. However, it's a little annoying, which leaves us with the issue of...what now?