If the textarea is bigger than the visible window and the caret (text cursor) moves outside of it, forcing it to scroll up or down, the scroll disappears until the mouse wheel is used. Same with pasting text from somewhere, even if it's not big enough to force scrolling.
I'd like to point out that the custom scroll isn't attached to the textarea, but to the textarea's wrapper.
If the textarea is bigger than the visible window and the caret (text cursor) moves outside of it, forcing it to scroll up or down, the scroll disappears until the mouse wheel is used. Same with pasting text from somewhere, even if it's not big enough to force scrolling.
I'd like to point out that the custom scroll isn't attached to the textarea, but to the textarea's wrapper.