Post comment button doesn't work when certain characters in comment

The post comment button cannot be clicked when certain characters are in a comment. A user tried to submit this comment:

"Some stores will never be suited for a cashier-less system (most obviously, retailers like Nordstrom) but it has application to plenty of other stores.”

The "post comment" button could not be clicked until the parenthesis were removed. I was able to add the parenthesis back in the Admin after the comment was submitted. We also had a user who could not submit until a dash was removed.

Some of our users type their comments in MS Word and other programs, and then paste them into the comment field. We never had this problem until recently.

What can I do to make sure the post comment button works no matter what characters are in the comment? Thanks