Text cursor moving to end of the message after mentioning someone

Ok so, I just started noticing this tonight, but since when does the text cursor move to the bottom of the message after adding a mention above? It wasn't doing this last night.

And as I run a racing simulation and only add the mentions at the end, it's getting increasingly frustrating to go back up every time I add one instead of just pressing down like I did before...

Of course, I see why this may be useful to some people, but could it at least be made into an option you can turn on or off?