Like others I noticed this capability was interfered with in some way. I had fun getting it to speak to me in a cheesy over-the-top Bostonian accent early on, then one day when I tried to demonstrate for a friend it interrupted itself mid-sentence, literally one voice speaking over the other truncated voice, saying something like "I'm sorry I can't mimic voices".

It seemed like they had one model monitoring the output of another model and then cutting it off when it crossed some line.