Automatic curly quotes – disable?

I'm using Clean Box and it automatically changes all quotation marks to curly quotation marks. This works fine until I'm blogging about code. If I try to insert a straight quotation mark using the insert special character option, clicking on the straight quote results in no mark entered even though all other marks work. Not sure why this mark is disabled, or how I can fix this. I have a child theme CSS built so if I know where this is I can change it in the child theme, but cannot find the possible culprit. Any thoughts?