I've had a similar experience. I also speak Italian and I found that Italians would speak to me in Italian unless I found myself struggling, at which point they'd offer to speak in English but wouldn't make the switch unless I agreed to it. I thought that was a polite way of going about it. But French people would sometimes reply in English at the very first instant that I make a mistake or fail to understand what they said (which could be due to them speaking too softly for me to hear them). It can be pretty annoying, to be honest, but that's just the way it is