The cursor is no longer shown at the end of lines that aren't the final one

This behavior was introduced in 1.21.6-pre4.

The bug

In multi-line text input fields such as writable books or the "Please describe what happened" edit box in player reporting screens, if you move the cursor to the end of a line that isn't the final one, it disappears.

In the screenshot attached, the cursor is to the right of "abc", yet it's invisible there.

Steps to reproduce

1. Write two lines of anything in a writable book.

2. With either your mouse or the arrow keys, move your cursor to the end of the first line.