Expanding comment box in IE

I’m using a tweaked-up version of the Journalized Blue template for my site, and it’s been called to my attention that on IE, when you begin typing a comment, the comment box expands all the way to the right of the page, and even allows typing beyond the right edge of the box before eventually wrapping to the next line.

Any thoughts what might cause this, and what I need to do to fix it??? The site is https://www.haveyoumettony.com

Thanks!