I'm sure I've mentioned this before but Spanish is my first language. When I visited Spain for the first time years ago, I stayed at a cousin's house for the 5 days I was there. I noticed I was naturally picking up their "lispy" accent towards the end of my visit, and when I returned home it stayed with me for a few days. I was a tad embarrassed because I didn't want people to think I was being stuck up or anything, but I just couldn't drop it on my own. 

I wonder if the same thing happens to, let's say Americans, when they visit a place like the UK or Australia.