A friend of mine is from Ireland and went to a Scandinavian country. Same story there: people would switch to English as soon as they found out that she's from Ireland. Her trick: "Sorry, I come from the Gaeltacht. My first language is Gaeilge."
I was mistaken for being American a lot. I'm pretty sure it was the default nationality to guess when they couldn't place an accent. Good to hear it wasn't just happening to me though ;)