Actually the selected text does usually match the copied text. It's just that some of the text is 0 font size so you don't know that you copied it.

Twitter does this on every single tweeted link. For example copy the link in this tweet: https://twitter.com/twitter/status/727507892283142145

You don't see a https:// on the page, but it gets put on your clipboard because it is actually there with 0 font size. In this case it's actually pointless though because they cut off the end of the url.

iTerm solves this problem from the other side- if you paste something that contains newlines, you get a confirmation dialog.

It defangs this vulnerability nicely.

The problem being that with this particular vulnerability, you do get the correct text in your clipboard initially, it's just overridden less than a second later.