[asciinema-player] `poster="data:text/plain,Say\n\rsomething"` won't result in line break/newline

On asciinema-player version 2.6.1, I tried

<asciinema-player rows="32" poster="data:text/plain,This will be printed as poster\n\rThis in second line" src="/asciicasts/temp.cast"></asciinema-player>

(see poster attribute) but I get
image

All the other poster attribute examples work so I was wondering if I did something wrong. Thank you!