If you start to select text in a TextArea and while selecting, move the cursor over the bounds of the TextArea (north of it), the selection area is not expanded.
This bug only appears to affect TextArea when the content has been scrolled as far down or as far up as possible. While the text is being vertically scrolled, selection works as expected.
A video showing the problem can be seen here: https://edvin.viewscreencasts.com/c97422da51ed4cf1845e5a7610a8716f
This bug makes it hard to select text in a TextArea, because one often moves the cursor further north than the TextArea when selecting.