I agree wholeheartedly with the French-English problem. I was in a French Immersion school for junior high and when I went to an English high school, I kept writing "environnement" and "gouvernement", as well as "labo" instead of "lab". Also, they'd managed to get me to think out my algebra in French so it was "x moins deux" instead of "x minus two" as I was doing my math homework!

Another side effect of my temporary French Immersion is that there are words which I first learned in French during that time, like "genocide", which I always hesitate before pronouncing in English because I'm likely to say it wrong.