No, that's normal. Accents are fluid and they change according to who you're with.

I live in an area with a particularly distinctive accent that I've mostly avoided. My best mate has a distinct tang of it and so does her mother, and when they're together their accent thickens to the point where I can barely understand them. Just like you imitate body language of the people around when you/in order to forge a connection with them, you do the same with linguistic cues, such as accent and vocabulary.