gemini tts won't switch voices

Here's my script:

STYLE DESCRIPTION:

NAR: smooth and steady. A narrator's voice.

BOBBY: amazingly deep Southwest Texas accent. Low pitched voice. Sounds like the cowboy he is.

SCRIPT:

NAR: Bobby pulled alongside on his John Deere 4430 and shut her down. He tugged off his straw hat and mopped his brow with the tail of his already-damp shirt.

BOBBY: [sighing] Whew! Gawd damn she a hot one!

NAR: he called

BOBBY: This here field's plum rough!

BOBBY: Gonna have to get me a smaller bra

BOBBY: [laughing] my boobs is a bobbin' around like them there boobs ain't sposed to be a doin'! [chuckle]

It always sticks with the first voice. I even tried swapping them, so NAR gets every line that BOBBY had, and BOBBY gets every line NAR had, and it just sticks with the voice I have BOBBY set up to use.

If I make a really short two line script that says something like:

NAR: I'm your narrator

BOBBY: I'm not your narrator

that seems to work. What's going on?