I cannot reproduce the behavior with one of my Kindle books on pc. However, I know that the accessibility features can behave differently whether you are accessing a Kindle book with an Iphone or a pc.
Have you tried switching off the TTS with Ctrl-t? Does this have an affect on NVDA?
Also, I have read somewhere that Kindle for pc needs enhanced type setting enabled in order for the accessibility features to work.
Just my two cents.