Does anyone know why when I edit my post with a quote in - I see a silly scrolling bar instead of everything fitting inside the "post"?

As above I go to edit one of the responses I posted to a post with a quote and my quotes end up being scrolled... Sometimes this happens even when I'm just quoting the first time around....

See below for example screenshot:

Any help would be really appreciated. It's starting to get on my nerves...

Best,

EW