Having a text field containing 41 lines of text (would fit on a single A4 page) I run into a limitation with highlighting text.

In this text field, 10 lines are highlighted - and that seems to be a limit.

If I try to highlight anything more I get the message “Your changes can not be applied as you have reached the text limit”.

I wonder that I still can make some text in that field bold without running into that limit.
Can anyone explain which limit I reached?