[Nogrod]

I read about a study years and years ago where they said that when facing emotionally charged situations (like telling someone you love her/him for the first time or asking for forgiveness in a highly envolved and embarrassing situation) people who come from a dialect-background and have adopted a kind of "common speech" after moving to a big city will revert into their dialects - or if they can hold themselves back from it, they feel that making those statements in the common speech is emotianally wrong in comparison with the dialect's way of expressing it would be.

That is not discussing people who would otherwise talk their dialect and only force themselves to speak the commong speech, but of people who have already adapted themselves to the new language surroundings and speak and think fluently or automatically the common way in normal situations... it's just that those exceptional circumstances bring their initial dialect to the fore.