tts page autoturn only works if built-in page number turns off for 1 page txt file

[CrazyGriferman]

My device is Verse Pro. I try to utilize the tts mode to learn new language. I create a txt file with only one page(a short story). And I import it into pocketbook. When I try to use tts. If you increase the font size, when you turn off the built-in page number, it will become multi-page and the page autoturn in tts works. If you turn on the built-in page number, even though you increate the font size, it's still one page. Under this circumstance, the page did not auto turn when reading the page(the sound is still playing).
I test a txt file with 2 pages or more. It worked even not turning off the built-in page number.
The language in txt file is Japanese.